Radox Reactions

REDOX REACTIONSHere, we will discuss about the different definitions of oxidation and reduction (redox) in terms of oxygen transfer, hydrogen and electrons. We will as well talk about oxidizing agent and reducing agent.Definitions of oxidation and reduction in terms of oxygen transfer• Oxidation is addition of oxygen.• Reduction is removal of oxygen.For instance, in the extraction of iron from its ore:Due to the fact that reduction and oxidation are going on side-by-side, this is known as a redox reaction meaning oxidation-reduction reaction.Oxidising and reducing agentsAn oxidizing agent is a substance that oxidizes another thing else. In the example above, the iron (III) oxide is the oxidizing agent.A reducing agent is a substance that reduces something else. In the above equation, the carbon monoxide is acting as the reducing agent.• Oxidizing agents provide oxygen to another substance.• Reducing agents take out oxygen from another substance.Oxidation and reduction in terms of hydrogen transfer• Oxidation is the loss of hydrogen from a compound.• Reduction is gain of hydrogen by a compound.These definitions you would notice are precisely the reverse of the definition of oxidation and reduction in terms of oxygen.For instance, ethanol can be oxidized to ethanal:In other to remove the hydrogen from the ethanol, you would need to make use of oxidizing agent. A regularly used oxidizing agent is potassium dichromate (VI) solution that is acidified with dilute sulphuric acid.Ethanal can as well again be reduced back to ethanol through the addition of hydrogen to it. A potential reducing agent is sodium tetrahydridoborate, NaBH4. Again, the equation is excessively complex to be worth troubling about at this level.As a summary:• Oxidizing agents provide oxygen to a different substance or take away hydrogen from it.• Reducing agents take away oxygen from another substance or provide hydrogen to it.Oxidation and reduction in terms of electron transfer• This is simply the most significant application of the oxidation and reduction at A’ level.• Oxidation is defined as electron loss.• Reduction is defined as electron gain.It is necessary that you have these definitions in mind. There is a extremely simple way to accomplish this.An example is shown below:The equation illustrates an uncomplicated redox reaction which can perceptibly be explained in terms of oxygen transfer.Copper (II) oxide and magnesium oxide are mutually ionic. The metals evidently are not. If you rephrase this as an ionic equation, it turns out that the oxide ions are bystander ions that you are left with:A last remark on oxidizing and reducing agentsIn the equation above, the magnesium is reducing the copper (II) ions by donating electrons to them to neutralize the charge. Magnesium is acting as a reducing agent.Looked at in another way, the copper (II) ions are extracting electrons from the magnesium to generate the magnesium ions. The copper (II) ions are working as an oxidizing agent.Oxidizing and Reducing AgentsAn oxidizing agent or oxidant is a substance that gains electrons and is reduced in a chemical reaction. The oxidizing agent is also known as electron acceptor, the oxidizing agent is usually in one of its top probable oxidation states due to the fact that it will gain electrons and be reduced. Examples of oxidizing agents are halogens, potassium nitrate, and nitric acid.A reducing agent or reductant is a substance that loses electrons and is oxidized in a chemical reaction. A reducing agent is normally in one of its lesser possible oxidation states and is referred to as the electron donor. A reducing agent would normally be oxidized due to the fact that it loses electrons in the redox reaction. Examples of reducing agents are the earth metals, formic acid, and sulfite compounds.A reducing agent reduces other substances and loses electrons; consequently, its oxidation state will amplify. An oxidizing agent oxidizes other substances and gains electrons consequently; its oxidation state will lessen.How to balance Oxidation-Reduction EquationsTrial-and-error approaches to balancing chemical equations entails playing with the equation amending the ratio of the reactants and products till the objectives below have been attained.Objectives for Balancing Chemical Equations1. The number of atoms of every element on both sides of the equation is identical and as a result mass is conserved.2. The sum of the positive and negative charges ought to be the same on both sides of the equation and consequently charge is conserved. Charge is conserved due to the fact that electrons are neither created nor destroyed in a chemical reaction.There are two scenarios where depending on trial and error can put you into trouble. Sometimes, the equation is extraordinarily complex to be calculated by trial and error within a realistic amount of time. Think about the following reaction, for instance.3 Cu(s) + 8 HNO 3 (aq) 3Cu 2+ (aq) + 2 NO(g) + 6 NO 3-(aq) + 4 H 2 O(l)Sometimes, more than a single equation can be printed that looks as it is balanced. The subsequent equations are just a handful of the balanced equations that can be written for the reaction between the permanganate ion and hydrogen peroxide, for instance.2 MnO 4-(aq) + H 2 O 2 (aq) + 6 H + (aq) 2 Mn 2+ (aq) + 3 O 2 (g) + 4 H 2 O(l) 2 MnO 4-(aq) + 3 H 2 O 2 (aq) + 6 H+(aq) 2 Mn 2+ (aq) + 4 O 2 (g) + 6 H 2 O(l) 2 MnO 4-(aq) + 3 H 2 O 2 (aq) + 6 H+(aq) 2 Mn 2+ (aq) + 5 O 2 (g) + 8 H 2 O(l) 2 MnO 4-(aq) + 7 H 2 O 2 (aq) + 6 H+(aq) 2 Mn 2+ (aq) + 6 O 2 (g) + 10 H 2 O(l)Equations like these ought to be balanced by an additional methodical approach than trial and error.Eletrochemical cellsGalvanic and Electrolytic CellsOxidation-reduction reaction or redox reactions occur in electrochemical cells. There are two different kinds of electrochemical cells. Spontaneous reactions take place in galvanic (voltaic) cells; non-spontaneous reactions take place in electrolytic cells. The two types of cells have electrodes where the oxidation and reduction reactions take place. Oxidation takes place at the electrode referred the anode and reduction takes place at the electrode known as the cathode.Electrodes and ChargeThe anode of an electrolytic cell is positive electrode while cathode is negative electrode, since the anode pull anions towards you from the solution. Nevertheless, the anode of a galvanic cell is negatively charged, since the spontaneous oxidation at the anode is the basis of the cell's electrons or negative charge. The cathode of a galvanic cell is its positive pole. In the 2cells- galvanic and electrolytic cells, oxidation occurs at the anode and electrons movement is from the anode to the cathode.Galvanic or Voltaic CellsThe redox or reduction-oxidation reaction in a galvanic cell is a spontaneous reaction. Therefore, galvanic cells are normally used as batteries. Galvanic cell reactions provide energy which is utilized to carry out work. The energy is harvested by positioning the oxidation and reduction reactions in different containers, connected by an apparatus that permits electrons to flow. A widespread galvanic cell is the Daniell cell, illustrated below.Electrolytic CellsThe redox reaction or reduction-oxidation reaction in an electrolytic cell is non spontaneous. Electrical energy is needed to stimulate the electrolysis reaction. A sample of an electrolytic cell is illustrated below with a molten NaCl that is electrolyzed to form liquid sodium and chlorine gas. The sodium ions wander toward the cathode, the electrode at which they are reduced to sodium metal. Likewise, chloride ions move to the anode and are oxidized to form chlorine gas. This sort of cell is used to generate sodium and chlorine. The chlorine gas can be gathered near the cell. The sodium metal is less heavy than the molten salt and is therefore taken away as it floats to the apex of the reaction container.Electrolysis is the passage of a direct electric current through an ionic compound that is either in molten form or dissolved in an appropriate solvent, leading to chemical reactions at the electrodes and disconnection of materials.The major components necessary to attain electrolysis are :• An electrolyte : An electrolyte is a substance that contains free ions that are the carriers of electric current in the electrolyte. If the ions are not in motion like in a solid salt electrolysis cannot take place.• A direct current (DC) supply: makes available the energy required to generate or discharge the ions in the electrolyte. Electric current is carried by electrons in the external circuit.• Two electrodes: Electrodes are electrical conductor that produces the physical boundary between the electrical circuit making available the energy and the electrolyte.Electrodes of metal, graphite and semiconductor substance are extensively used. Selection of appropriate electrode depends on chemical reactivity between the electrode and electrolyte and the asking price of production.Process of electrolysisThe main process of electrolysis is the substitution of atoms and ions through the removal or addition of electrons from the external circuit. The preferred products of electrolysis are frequently in a dissimilar physical state from the electrolyte and can be separated by a number of physical processes. For instance, in the electrolysis of brine that yields hydrogen and chlorine, the resulting product are gaseous. These gaseous products bubble from the electrolyte and are collected.2 NaCl + 2 H 2 O → 2 NaOH + H 2 + Cl 2A liquid containing mobile ions (electrolyte) is manufactured by:• Solvation or reaction of an ionic compound with a solvent like water to give rise to mobile ions.• An ionic compound is dissolved or merged by heatingAn electrical potential is applied crosswise a pair of electrodes engrossed in the electrolyte.Every one of the electrodes attracts ions that have differing charge. Positively charged ions (cations) move towards the electron-supplying (negative) cathode, while negatively charged ions (anions) drift towards the positive anode.At the electrodes, electrons are taken or given out by the atoms and ions. Those atoms that gain or lose electrons to turn into charged ions move into the electrolyte. Those ions that gain or lose electrons to turn into uncharged atoms split from the electrolyte. The production of uncharged atoms from ions is referred to as discharging.The energy that is needed to make the ions to travel to the electrodes, and the energy to result to the change in ionic state, is made available by the external supply of electrical potential.Oxidation and reduction at the electrodesOxidation of ions or neutral molecules takes place at the anode, and the reduction of ions or neutral molecules takes place at the cathode. For instance, it is probable to oxidize ferrous ions to ferric ions at the anode:Fe 2+ aq → Fe 3+ aq + e -It is as well likely to reduce ferricyanide ions to ferrocyanide ions at the cathode:Fe(CN)3-6 + e– → Fe(CN)4-6

Rate of Chemical Reaction

1. Rates Of Reactions And Equilibrium Of Reacting SystemsChemical equilibrium in a chemical reaction is the condition in which both reactants and products are present at concentrations that have no extra propensity to alter with time. Characteristically, this situation arises when the rate of forward reaction is equal to the rate of backward reaction. The rate of forward and backward reaction is not normally zero at this point but is equal. What this means is that there is no net alterations in the concentrations of the reactant(s) and product(s). A situation like this is referred to as dynamic equilibrium.Reversible reactionsA reversible reaction is a reaction which can proceed at either direction depending on the situations.If you pass steam over hot iron, you would notice a reaction between the steam and the iron to produce a black, magnetic oxide of iron referred to as triiron tetroxide, Fe 3 O 4The hydrogen that is manufactured during the reaction is carried away by the stream of steam.Under various situations, the products of this reaction will as well react together. The Hydrogen that is made to pass over hot triiron tetroxide reduces it to iron. Steam is also manufactured.At this juncture the steam produced in the reaction is taken away by the stream of hydrogen.These reactions occur simultaneously either ways and are reversible, but under the conditions usually used, they turn out to be one-way reactions.Reversible reactions taking place in a closed systemA closed system is a system is a reacting system in which no substances are added to the system or lost from it. Energy can, nevertheless, be transmitted in or out freely.If we consider the example we've considering above, imagine that iron is being heated in steam in a closed container. The system is being heated up but none of the substances in the reaction can break out because the system is closed. As the amount of triiron tetroxide and hydrogen begin to be formed, they would in turn react again to produce the original iron and steam. Therefore, if you analyzed the mixture after sometime you would notice a situation referred to as a dynamic equilibrium.In a nutshell, a dynamic equilibrium takes place when a reversible reaction occurs in a closed system. The system remains unchanged except that energy would be added to it. When the reaction is at equilibrium, the amount of all that is available in the mixture remains unchanged even though the reactions are still progressing. This situation arises due to the fact that at this point, the rate of forward reaction is equal to the rate of backward reaction.If there is any alteration in the conditions to the extent that it alters the relative rates of the forward and backward reactions, the position of equilibrium is shifted to annul the changes in the conditions.Reaction Rate or rate of a chemical reactionThe rate of a chemical reaction or Reaction Rate is the estimation of the alteration in concentration of the reactants or the alteration in concentration of the products over a unit time.For an example, during the chemical reaction between products A and B as shown in the equation below, the reactants A and B are used up while the concentration of product AB increases. The reaction rate or rate of the chemical reaction can be measured by estimating how fast the concentration of A or B is being used up, or by how fast the concentration of AB is being formed.A + B ---- ABFor the purpose of stochiometry, the above equation can be further represented as:aA + bB ------ cC+ dDCollision TheoryThe collision theory states that gaseous state chemical reactions takes place when two gas molecules smash together with enough kinetic energy. The smallest amount of energy that is needed for a thriving collision, which leads to a successful reaction, is referred to as the activation energy. Consequently, only a fraction of collisions result to successful reactions.The collision theory is derived from the kinetic theory of gases. Thus we are only dealing with gaseous chemical reactions. Because of this, the ideal gas assumptions are applied. Moreover, we are as well making assumptions that:1. All the reacting molecules are moving through space in a straight line.2. All molecules are inflexible spheres.3. The reactions being discussed only takes place between two molecules.4. The molecules ought to collide with one another.In the end, the collision theory of gases offers us the rate constant for bimolecular gaseous reactions; it is equal to the rate of winning collisions. The rate of successful collisions is proportional to the small part of successful collisions multiplied by the general collision frequency.Collision FrequencyThe rate or frequency at which molecules collide is referred to as the collision frequency, Z. The unit of collision frequency is collisions/ unit of time. Given a box of molecules A and B, the collision frequency between molecules A and B is given by:Successful CollisionsTo enable a successful collision to take place, the molecules of the reactant ought to collide with sufficient kinetic energy to break original bonds and be able to form fresh bonds to turn into the molecules of the product. Therefore, it is referred to as the activation energy for the reaction; it is as well normally regarded as the energy barrier.The portion of collisions that possess sufficient energy to exceed the activation barrier is denoted as:The tiny proportion of successful collisions is directly proportional to the temperature and inversely proportional to the activation energy of the reaction.In conclusionThe rate constant of a gaseous reaction is proportional to the product of the collision frequency and the fraction of successful reactions. Just like we mentioned above, enough kinetic energy is necessary for a successful reaction; but they need to appropriately.The Activation Energy of Chemical ReactionsOnly a minute portion of the collisions between reactant molecules change the reactants into the products of the chemical reaction. This can be understood by considering the reaction between ClNO2 and NO.ClNO 2 (g) + NO(g) NO 2 (g) + ClNO(g)During the process of this reaction, a chlorine atom is transmitted from one nitrogen atom to another. To enable the reaction to occur, the nitrogen atom in NO have to bump with the chlorine atom in ClNO2The reaction will not take place if the oxygen end of the NO molecule collides with the chlorine atom on ClNo 2It will also not take place if an oxygen atom from among the 2 atoms on ClNO2 collides with the nitrogen atom on NO.An additional factor that determines if a reaction will take place is the energy the molecules carry or bears the moment they come in contact for collision. It is not every molecule that possesses the same kinetic energy. This is significant for the reason that the kinetic energy molecules bear the moment they bump is the most important basis of the energy that ought to be invested in a reaction to make it to occur.The total typical free energy for the reaction between ClNO2 and NO is favorable.ClNO 2 (g) + NO(g) NO 2 (g) + ClNO(g) Go = -23.6 kJ/molBut, prior to the reactants being converted into products, the free energy of the system ought to conquer the activation energy for the reaction.All molecules have a definite minimum quantity of energy. The energy can either be in the form of Kinetic Energy and/or Potential Energy. When molecules come in contact with one another, the kinetic energy of the molecules can be made use of to elongate, twist, and eventually break bonds, resulting to chemical reactions. If molecules are travelling too unhurriedly with a small kinetic energy, or they collided with an inappropriate direction, they will not lead to reaction and would merely bounce away from each other. Nevertheless, if the molecules are travelling at a swift speed sufficient to cause a successful collision orientation, in a manner that the kinetic energy on collision is higher than the minimum energy barrier, then a reaction will take place. The minimum energy obstruction that ought to be achieved for a chemical reaction to occur is known as the activation energy; Ea. Ea is normally in units of kilojoules per mole.Activation energy, Enthalpy, Entropy and Gibbs EnergyIn Thermodynamics, Gibbs free energy change, ΔG, is defined as:ΔG=ΔH −TΔSwhere• ΔG = Gibbs free energy change of the reaction• ΔH = Enthalpy change of the reaction• ΔS = Entropy change of the reaction.ΔGo is the Gibbs energy change when the reaction takes place at Standard State (1 atm, 298 K, pH 7).To calculate a change in Gibbs free energy of the reaction that did not occur at a standard state, the Gibbs free energy equation can be denoted as:ΔG = ΔGo + RTlnkwhere• ΔG = Gibbs free energy change of the reaction• ΔGo = standard Gibbs free energy of the reaction• R = 8.314 J/molK• k = equilibrium constantAt equilibrium, ΔG=0. The equation above then becomes:0= ΔGo + RTlnkSolve for ΔGoΔGo = −RTlnkDynamic EquilibriumAt dynamic equilibrium, reactants are transformed to products and products are transformed to reactants at an equivalent and constant rate. An example of a reaction in dynamic equilibrium is the dissociation of acetic acid. For instanceCH 3 COOH ---- H+ + CH 3 COO-Static EquilibriumStatic equilibrium is as well referred to as mechanical equilibrium. It takes place when all particles in the reaction are at rest and there is no movement between reactants and products. Static equilibrium can as well be experienced in a steady-state system in a physics-based outlook.Dynamic forces are not performing on the potential energies of the backward and forward reactions. One example of static equilibrium is graphite changing into diamond. This reaction is well thought-out at static equilibrium after it takes place for the reason that there is no more forces acting upon the reactants (graphite) and products (diamond).Le Chatelier's Principle and EquilibriumEquilibrium can be explained through the Le Chatelier's principle. The kinetics of a reaction can alter and the position of equilibrium would depend on the properties of the reactants and products. Put in a simpler way, the equilibrium will swing towards one side or the other relative to the concentration, temperature, pressure, and volume. Le Chatelier's principle is not the same thing as dynamic equilibrium. Although they are comparable, they are of variable concepts. Le Chatelier's principle explains the way equilibrium can alter. Dynamic and static equilibrium explain the way systems in equilibrium behave.Comparison between Dynamic and Static EquilibriumA reaction at dynamic equilibrium has the capability to be reversible while a reaction at static equilibrium is irreversible. The equilibrium constant alone cannot determine if a reaction is in static or dynamic equilibrium due to the fact that the equilibrium constants are estimated through the concentrations of products against reactants. A reaction is at dynamic equilibrium if the rate of the forward reaction is the same as the rate of the backward reaction. It is at static equilibrium if the reaction has taken place and there is no forward or backward rate of reaction.

Acid Bases And Salt For Chemistry Students

ACID BASE AND SALTSVarious definitions of Acids and BasesThere are various definitions of acids and bases. Although these definitions don't disagree with one another, they differ in their comprehensiveness. Apart from the already established definitions of Acids, bases and salts Antoine Lavoisier, Humphry Davy, and Justus Liebig as well discovered few things about acids and bases, but they didn't make their definitions formal.Svante Arrhenius defined acid in terms of their behavior in water.In 1884 Svante Arrhenius observed that salts like NaCl dissociate in water to provide particles he called ions.H 2 ONaCl(s) Na+(aq) + Cl-(aq)3 years after that he extended his theory by explaining that acids are neutral compounds that ionize when they dissolve in water to give H+ ions and an equivalent negative ion. His theory describes hydrogen chloride as an acid because it ionizes in aqueous solution to produce hydrogen (H+) and chloride (Cl-) ions as s demonstrated below:H2OHCl(g) H+(aq) + Cl-(aq)In summary, his theory of acids states that:• Acids are compounds which generate H+ ions in aqueous solutions eg.• Bases are compounds which generate OH- ions in aqueous solutions• His definition only works in the presence of water. The definition is only valid in aqueous solutions.• His definition only allows protic acids that are able to produce hydrogen ionsThe definition also only allows hydroxide bases.Arrhenius also dispute that bases are neutral compounds that also dissociate or ionize in water to produce OH- ions and a positive ion. NaOH is an example of Arrhenius base due to the fact that it dissociates in water to give the hydroxide (OH-) and sodium (Na+) ions.H2ONaOH(s) Na+(aq) + OH-(aq)An Arrhenius acid is therefore any material that ionizes when dissolved in water to produce the H+, or hydrogen ion.An Arrhenius base is therefore any material that produces the OH-, or hydroxide, ion when dissolved in water.Examples of Arrhenius acids are compounds like HCl, HCN, and H2SO4 that ionize in water to produce H+ ion. Examples of Arrhenius bases are ionic compounds that have the OH- ion, like NaOH, KOH, and Ca(OH)2.The Arrhenius theory explains the reason why acids posses related properties. The distinguishing properties of acids are as a result of the presence of the H+ ion produced when an acid is dissolved in water. It also gives explanation to why acids neutralize bases and why bases neutralize acids. Acids supply the H+ ion; bases supply the OH- ion; and these two ions join together to form water.H+(aq) + OH-(aq) H 2 O(l)Disadvantages of the Arrhenius theory1. It can be relevant only to reactions that take place in water because it defines acids and bases in terms of their behavior when dissolved in water.2. It gives no explanation to why a number of compounds that has hydrogen with an oxidation number of +1 like HCl dissolve in water to yield acidic solutions, while others like CH 4 don’t.3. It is just the compounds that hold the OH- ion that are graded as Arrhenius bases. The Arrhenius theory does not give explanation to why compounds like Na2CO3 have the distinguishing properties of bases.Johannin es Nicolaus Brønsted - Thomas Martin Lowry theory of acid defined acids as• Proton donors and• Bases as proton acceptors• The definition also works in aqueous solutions• The definition works for bases apart from hydroxide bases.• The definition only allows protic acids.Gilbert Newton Lewis defined• Acids as electron pair acceptors• Bases as electron pair donorsProperties of Acids1. Acid tastes sour and must not be tasted.2. Acids turn blue litmus paper to red.3. Aqueous solutions of acids conduct electric current. They are therefore good electrolytes4. Acids react with bases to form salts and water5. Acids give out hydrogen gas when they are reacted with an active metal like alkali metals, alkaline earth metals, zinc and aluminum.Properties of Bases1. Bases taste bitter and must not be tasted2. They sense slippery or foamy. You must not by chance feel them3. Bases don't alter the color of litmus paper but can they can turn red or acidified litmus paper to blue4. Aqueous solutions of bases conduct electricity and are therefore good electrolytes.5. Bases react with acids to form salts and waterExamples of regular Acids• Citric acid from particular fruits and vegetables especially citrus fruits• ascorbic acid-vitamin C from as from certain fruits• vinegar which contains about 5% acetic acid• carbonic acid that are useful during the carbonation process of soft drinks• lactic acid is available in buttermilkExamples of regular Bases• Detergents• Soap• Soduim hydroxide (NaOH)• Aqueous ammoniapH and pH MeterIn chemistry, pH is an evaluation of the acidity or basicity of an aqueous solution. Solutions that have a pH value that is below 7 are said to be acidic and solutions that have pH value greater than 7 are considered basic or alkaline. The pH of pure water is about 7.Acid-Base IndicatorsWeak Acids and Bases can be used as Acid-Base indicator. An acid-base indicator is a weak acid or a weak base. An Indicator acid base indicator does not change color from pure acid to pure alkali solution at particular hydrogen ion concentration, but to a certain extent, color change takes place over a range of hydrogen ion concentrations. This range is termed the color change interval and is articulated as a pH range.The use of acid base indicatorsWeak acids are titrated in the presence of indicators that alter a little in alkaline situations. Weak bases ought to be titrated in the presence of indicators that alter their colours under a little acidic condition.Popular acid-base indicators:Examples of acid-base indicators are:• Thymol blue• tropeolin OO• methyl yellow• methyl orange• bromphenol blue• bromcresol green• methyl red• bromthymol blue• phenol red• neutral red• phenolphthalein• thymolphthalein• alizarin yellow• tropeolin O• nitramin• trinitrobenzoic acid.Common Acid-Base Indicators pHIndicator Range 1.2-Thymol Blue2.8 11.2-Pentamethoxy red2.3 1.3-Tropeolin OO3.2 1.3-Tropeolin OO3.2 2.4-2,4-Dinitrophenol4.0 2.9-Methyl yellow4.0 3.1-Methyl orange4.4 3.0-Bromphenol blue4.6Tetrabromphenol 3.0-4.6 blueAlizarin sodium 3.7- sulfonate5.2 3.7-α-Naphthyl red5.0p- 3.5-5.5EthoxychrysoidineHydrolysisHydrolysis is a chemical reaction that results to molecules of water (H2O) being divided into hydrogen cations H+ and hydroxide anions (OH−) in the process of a chemical reaction. The cation is usually known as protons. Hydrolysis is the kind of reaction that is used to break down definite polymers, principally those prepared by step-growth polymerization. Such dilapidation of polymer is frequently catalyzed by either acid or alkali example concentrated sulfuric acid (H2SO4) and sodium hydroxide (NaOH) respectively.Types of hydrolysisHydrolysis is a chemical reaction in which a particular molecule is divided into two parts with the addition of one molecule of water. One part of the reacting molecule gains a hydrogen ion (H+) through the water molecule added. The remaining part takes up the other hydroxyl group (OH−).The most widespread hydrolysis takes place when a salt of a weak acid or /and a weak base is dissolved in water. Water automatically ionizes into negative hydroxyl ions and positive hydrogen ions. The salt splits into positive and negative ions. For instance, sodium acetate in water dissociates into sodium and acetate ions. Sodium ions react sparingly with hydroxyl ions while acetate ions join with hydrogen ions to form neutral acetic acid, and the overall result is a comparative overload of hydroxyl ions, resulting to a basic solution.Nevertheless, under standard conditions, just a small number of reactions occur between water and organic compounds. Commonly, strong acids or bases have to be incorporated to be able to attain hydrolysis where water has no consequence. The acid or base would act as a catalyst. They are used to hasten up a reaction but they remain unchanged at the end of the reaction.Acid–base catalyzed hydrolyses reaction are extremely widespread. An instance is the hydrolysis of amides or esters. Their hydrolysis takes place when the nucleophile ie nucleus hunting agent, for example water or hydroxyl ion reacts with the carbon of the carbonyl group of the ester or amide. In an aqueous base solution, hydroxyl ions are more of better nucleophile than dipoles like water. In acid, the carbonyl group becomes protonated which results to a better nucleophilic attack. The products for the two types of hydrolysis reaction are compounds with carboxylic acid groups.Acidic, Basic, and Neutral SaltsSome examples of Ions of Neutral SaltsCationsNa + + K + Rb + Cs +Mg 2+ Ca 2+ Sr 2+ Ba 2+AnionsCl -Br -I -,ClO 4 -BrO 4 -ClO 3 -N0 3 -A salt is a compound formed when an acid is reacted with a base. Normally, a neutral salt is formed when a strong acid neutralizes a strong base in the reaction. See example below:H+ + OH- = H2OThe passerby ions in an acid-base reaction result into a salt solution. The majority of neutral salts contain cations and anions listed below: They have less affinity with water. Therefore, salts that contain any of these ions are neutral salts. For instance: NaCl, KNO3, CaBr2, CsClO4 are neutral salts.Acidic IonsNH 4 + Al 3 + Pb 2 + Sn 2 +Transition metal ionsHSO 4 -H 2 PO 4 -Basic IonsF -C 2 H 3 O 2 -NO 2 -HCO 3 -CN -CO 3 2-S 2 -SO 4 2-HPO 4 2-PO 4 3-During a reaction between weak acids and bases, the comparative strength of the reacting acid-base pair in the salt establishes the pH of the solutions. The salt, or the solution of the salt formed can either be acidic, neutral or basic. Acid salt is formed between a strong acid and a weak eg. NH4Cl.Abasic salt is formed between a weak acid and a strong base .eg. NaCH3COO.Hydrolysis of Acidic SaltsAcid salt is formed between a strong acid and a weak eg. NH4Cl. Ammonia is a weak base, and a salt of ammonia with every strong acid result to a solution with a pH below 7. For instance in the reaction between hydrocholic acid and ammonia below:HCl + NH 4 OH = NH 4 + + Cl -+ H 2 OHere, the NH 4 + ion reacts with water through the process of hydrolysis as shown in the equation below:NH 4 + + H 2 O = NH 3 + H 3 O + .The acidity constant can be obtined from Kw and Kb.[H 3 O + ] [NH 3 ] [OH -]Ka = ---------------- ------[NH 4 + ] [OH -]= Kw / Kb= 1.00e-14 / 1.75e-5 = 5.7e-10. Where a =acid, b =base and w = water.

what is Stoichometry And Chemical Reaction

STOICHIOMETRY AND CHEMICAL REACTIONSStoichiometry is a branch of chemistry that is concerned with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relationship among quantities of reactants and products characteristically form a ratio of positive numerals. For instance, in a chemical reaction that forms ammonia (NH 3 ), precisely 1 molecule of nitrogen gas (N 2 ) reacts with 3 molecules of hydrogen gas (H 2 ) to generate 2 molecules of NH 3 . See below:N2 + 3H2 → 2NH3This type of stoichiometry which describes the quantitative relationships between substances when they take part in chemical reactions is referred to as reaction stoichiometry. In the above sample reaction, reaction stoichiometry explains the 1:3:2 molecular rations of nitrogen, hydrogen, and ammonia.Stoichiometry can be employed to estimate quantities like the amount of products in mass, moles and volume that can be produced with given reactants and percentage yield. This means the percentage of the particular reactant that is converted into the product. Stoichiometry extimations can guess the way elements and components diluted in a standard solution react in experimental conditions.Stoichiometry is founded on the law of conservation of mass which states that the mass of all the reactants in a chemical reaction is equivalent to the mass of the products.Composition stoichiometry explains the quantitative (mass) relationships between elements that make up a compound. For instance, composition stoichiometry explains the nitrogen to hydrogen ratio in the compound ammonia (NH3): 1 mol of ammonia is composed of 1 mol of nitrogen and 3 mol of hydrogen. As the nitrogen atom is roughly 14 times heavier than the hydrogen atom, the mass ratio is 14:3; consequently 17 kg of ammonia is composed of 14 kg of nitrogen and 3 kg of hydrogen.A stoichiometric amount or stoichiometric ratio of a reagent is the most favorable amount or ratio at which the reaction proceeds to completion and in which1. Every one of the reagent is used up2. There is no shortage of the reagent3. There is no surplus of the reagent.A non-stoichiometric mixture, which the chemical reaction has reached the completion, is liable to have only the restrictive reagent consumed completely.Although nearly all chemical reactions possesses integer-ratio stoichiometry in amount of matter units -moles, number of particles, a few non stoichiometric compounds that cannot be shown ratios of distinct intergers are available. These substances, consequently, go against the law of definite proportions that forms the foundation of stoichiometry together with the law of multiple proportions.Gas stoichiometry deals with reactions involving gases, where the gases are at a known temperature, pressure, and volume, and can be assumed to be ideal gases. For gases, the volume ratio is ideally the same by the ideal gas law, but the mass ratio of a single reaction has to be calculated from the molecular masses of the reactants and products. In practice, due to the existence of isotopes, molar masses are used instead when calculating the mass ratio.Laws of chemical combinationIt was an Englishman of the 17th century known as Robert Boyle who after his research and findings on the behaviour of gases, made available an unambiguous evidence for the atomic composition of matter. He was the foremost to describe an element as a material that cannot be chemically broken down into a simper form. He was of the opinion that a number of dissimilar elements might exist in nature.Laws of chemical combinationThe fundamental laws of chemical combination are:• The law of conservation of mass• The law of constant composition, and• The law of multiple proportions.The law of conservation of massThis law states that the mass of a closed system will stay constant over time, in spite of the processes acting within the system. A comparable statement is that mass cannot be created/destroyed, despite the fact that it can change into one form or the other. This means for any chemical process in a stopped up system, the mass of the reactants must be the same with the mass of the products.Law of constant compositionThe law of constant composition states that the composition of a particular substance is always the same, in spite of the way the substance was made or wherever the substance exists. If take water for instance, it is known that a molecule of water always consist of 2 atoms of hydrogen and 1 atom of oxygen. Whenever the composition of a molecule alters, the result will no longer be the same substance but a different one possessing different properties.The law of multiple proportionsThe law of multiple proportions states that when elements combine to form compounds they do so in a ratio of minute whole numbers. For instance carbon and oxygen react to form CO or CO2, but not in fractions like CO1.2. In addition, the law states that if two elements form more than one compound between them; then the ratios of the masses of the second element united with a fixed mass of the foremost element will as well exist in ratios of small non-fractional integers.Types of Chemical EquationsA chemical equation is composed of chemical formulas of the reactants -the reacting substances and the chemical formula of the products- the substances created during the chemical reaction. The two are alienated by an arrow symbol which is normally read as "yields" and every individual substance's chemical formula is alienated from the rest by a plus sign.For an example, the equation for the reaction of hydrochloric acid with sodium can be shown as:2 HCl + 2 Na → 2 NaCl + H 2It is highly crucial for a chemist to be capable of writing accurate balanced equations and to interpret equations written by others. It is also extremely useful for him or her to be aware of the way to foretell the products of some specific types of reactions.A Chemical Equation shows:1. The reactants which combine together in the reaction.2. The products which are created by the reaction.3. The amounts of every substance used and every substance formed.Two significant principles to bear in mind when writing a chemical equation:1. Every chemical compound has a formula which cannot be changed.2. A chemical equation gives account of all the atoms used in the chemical reaction. This is an application of the Law of Conservation of Matter. It states that in a chemical reaction atoms are neither created nor destroyed.C. A few things to bear in mind about writing equations:1. The diatomic elements when they stand alone are always written as H2, N2, O2, F2, Cl2, Br2 and I22. The sign, →, is used to denote "yields" and illustrates the direction of the action.3. A minute delta, ( ), on top of the arrow illustrates that heat has been supplied.4. A double arrow, ↔, illustrates that the reaction is reversible and can move in both directions.5. Before starting to balance an equation, crosscheck every one of formulas to ensure that they are right. You must never alter a formula all through the balancing of an equation.6. Balancing of an equation is done by putting coefficients in front of the formulas to make sure you have got equivalent number of atoms of everyone of the element on the two sides of the arrow.Four basic types of chemical reactionsA. Synthesis or composition reaction:• In this type of reaction, two or more elements or compounds may mingle to form a more complex compound.The basic formula for this type of reaction is : A + X → AXSome instances of synthesis reactions are:1. Metal + oxygen → metal oxideEX. 2Mg(s) + O 2 (g) → 2MgO(s)2. Non-metal + oxygen → nonmetallic oxideEX. C(s) + O 2 (g) → CO 2 (g)3. Metal oxide + water → metallic hydroxideEX. MgO(s) + H 2 O(l) → Mg(OH) 2 (s)4. Non-metallic oxide + water → acidEX. CO 2 (g) + H 2 O(l) → ; H 2 CO 3 (aq)5. Metal + non-metal → saltEX. 2 Na(s) + Cl 2 (g) → 2NaCl(s)6. A few nonmetals combine with each other.EX. 2P(s) + 3Cl 2 (g) → 2PCl 3 (g)You ought to know these two reactions and try to remember them:N 2 (g) + 3H 2 (g) → 2NH 2 (g)1. NH 3 (g) + H 2 O(l) → NH 4 OH(aq)B. Decomposition reaction:• In a decomposition reaction, one compound breaks down into its component parts or simpler compounds.Basic equation formula for this type of reaction is AX → A + XSome instances of decomposition reactions are1. Metallic carbonates, when heated, form metallic oxides and CO 2 (g).EX. CaCO 3 (s) → CaO(s) + CO 2 (g)2. The majority metallic hydroxides, when heated, decompose to form metallic oxides and water.EX. Ca(OH) 2 (s) → CaO(s) + H 2 O(g)3. Metallic chlorates, when heated, decompose to form metallic chlorides and oxygen.EX. 2KClO 3 (s) → 2KCl(s) + 3O 2 (g)4. Some acids, when heated, decompose to form non metallic oxides and water.EX. H2SO4 → H 2 O (l) + SO 3 (g)C. Replacement reaction:• A more reactive element takes the place of another element in a compound and frees the less active one.• Basic form: A + BX → AX + B or AX + Y → AY + XExamples of replacement reactions1. Replacement of a metal in a compound by a more active metal.EX. Fe(s) + CuSO 4 (aq) → FeSO 4 (aq) + Cu(s)2. Replacement of hydrogen in water by an active metal.EX. 2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g)EX. Mg(s) + H 2 O(g) → MgO(s) + H 2 (g)3. Replacement of hydrogen in acids by active metals.EX. Zn(s) + 2HCl(aq) → ZnCl 2 (aq) + H 2 (g)4. Replacement of nonmetals by more active nonmetals.EX. Cl 2 (g) + 2NaBr(aq) → 2NaCl(aq) + Br 2 (l)D. Ionic:• This takes place among ions in aqueous solution. The reaction will take place when one pair of ions approach together to create at least one among the following:1. a precipitate2. a gas3. Water or a number of other non-ionized substances.Basic form of the equation: AX + BY → AY + BXSome examples of ionic reactions:1. Formation of precipitate.EX. NaCl (aq) + AgNO 3 (aq) → NaNO 3 (aq) + AgCl(s)EX. BaCl 2 (aq) + Na 2 SO 4 (aq) → 2NaCl(aq) + BaSO 4 (s)2. Formation of a gas.EX. HCl(aq) + FeS(s) → FeCl 2 (aq) + H 2 S(g)3. Formation of water. When a reaction takes place between an acid and a base, the reaction is known as a neutralization reaction.)EX. HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l)EMPIRICAL AND MOLECULAR FORMULAEThe empirical formula of a compound is the simplest formula of that compound. A molecular formula is the equivalent to or is a multiplication of the empirical formula, and is focused on the definite number of atoms of every type in the compound. For instance, if the empirical formula of a compound is C3H8, its molecular formula might be be C3H8 , C6H16 and so on .

Stability of Substances

SOLUBILITY OF SUBSTANCESThe solubility of a substance is the amount of a substance that will dissolve in a given amount of a solvent. Solubility is a quantitative term. Solubility of substance differs greatly. The terms soluble and insoluble are comparative. A compound is termed soluble if more than 0.1g of that compound dissolves in 100 mL of solvent. If less than 0.1 g of the compound dissolves in 100 mL solvent, the compound is said to be insoluble or sparingly soluble. The terms miscible and immiscible liquids that are encountered when describing the solubility of a liquid in another mean: a liquid is miscible when it is soluble beyond measure for instance alcohol is miscible with water. A liquid is immiscible or insoluble means the same thing; oil is said to be immiscible with water, as in oil and vinegar salad dressing.Determination of SolubilityTo determine solubility, a known amount of a solvent such as 100 mL is put in an urn after which the substance whose solubility is to be calculated is added until the substance is unable to dissolve again even when stired vigorously and left to stand for a long period of time. Such a solution is said to be saturated meaning that it contains as much solute that it could dissolve at that temperature.Saturated solutionsA saturated solution is a solution that contains the dissolved solute in equilibrium.Dissolution and precipitation occurs at the same rate, thus satisfying the condition for a dynamic equilibrium. This condition was set forth when discussing the equilibrium between liquid and vapor. We can convey equilibrium condition in sucrose solution for an example with the equation below:Sucrose(s) ----- Sucrose(aq)Two deductions that can be made from the equations are that the two processes of dissolution and precipitation are taking place concurrently and that the number of molecules in the solution remains unchanged.The saturated solution of an ionic compound differs a little from the saturated solution of covalent compounds such as sucrose. The ionic compound melts and stays in solutions as ions while the covalent compound melts and remains in solutions as molecules. The equilibrium of sodium chloride with its ions in a saturated solution is demonstrated with the following equation:NaCl(s) Na+(aq) + Cl-(aq)An unsaturated solution normally has smaller amount of solute than a saturated solution. There is nothing like equilibrium in an unsaturated solution. Such a solution would normally take up and dissolve any additional solute that is added to it. On the contrary when you add an extra amount of solute to a saturated solution, no additional number of solute would be dissolved because it has reached the boundary of its solubility. Any extra solute added to a saturated solution would merely amplify the amount of undissolved solute.It is worth noting that solubility alters with temperature. A solution that is saturated at a particular temperature may be unsaturated at another temperature.Again, dissolution requires interaction between the molecules (or ions) of the solute and the molecules of the solvent. A thinly divided solute will dissolve more quickly than when it is larger due to the fact that it provides a better contact between the dissolving solute and solvent. Constant stirring also increases the rate of dissolution, due to the fact that stirring alters the particular solvent molecules that are come in contact with undissolved solute. Solubility of solids and liquids characteristically increases with increase in temperature, therefore, temperature, solids and liquids are frequently dissolved in warm solvents.Factors affecting solubility of substanceThere are a lot of factors that affect the solubility of a substance in another. Some of them are: temperature, polarity, pressure, and molecular size.1. Forces between particlesThe nature of intermolecular forces in both the solute and the solvent determines the rate of solubility between them. When a substance dissolves in another, it must overcome the attractive forces between two of them. The dissolving solute ought to be able to break up the aggregation of molecules in the solvent. This means overcoming the hydrogen bonds between the molecules or the dispersion forces between molecules in a non-polar solvent. The molecules of the solvent must therefore have enough attraction for the particles of the solute to take them away one after another from their neighbors in the undissolved solute. If the solute is ionic, only an extremely polar solvent such as water provides enough interaction to result to dissolution. If the solute particles are polar molecules, they are easily dissolved in polar solvents like alcohols. Non polar solute on the other hand dissolves in non-polar solvents. The reason is not because polar solvent molecules cannot conquer the weak dispersion forces between the solute molecules, but due to the fact that these dispersion forces are extra ordinarily weak to overcome the dipole-dipole interaction that exists between the solvent molecules.Generally, like dissolves like. Ionic and polar compounds are soluble in polar solvents like water or liquid ammonia. Nonpolar compounds are soluble in non-polar solvents, like carbon tetrachloride, and hydrocarbon solvents like gasoline.The solubility of gases in water depends very much how polar the gas molecules are. Those gases whose molecules are polar are much more soluble in water than non-polar gases. Ammonia, a highly polar molecule, is extremely soluble in water (89.9 g/100 g H2O) and hydrogen chloride (82.3 g/100 g H2O). Helium and nitrogen are nonpolar molecules. Helium is mere partially soluble (1.8 X 10-4 g/100 g H2O), like in nitrogen (2.9 X 10-3 g/100 g H2O)Solubility and inter-particle bonds in various types of compounds and their relative solubilities in water, a polar solvent; in alcohol, a less polar solvent; and in benzene, a non-polar solventKinds of bonds Example Water Alcohol Benzeneionic sodium chloride very soluble slightly soluble insolublepolar covalent sucrose (sugar) very soluble soluble insolublenonpolar covalent napthalene Insoluble soluble very soluble2. TemperatureThe solubility of substances varies at different temperature. Usually, the solubility of solids and liquids rises at higher temperature but the solubility of gases diminishes with an increase in temperature. This property of gases causes is a great concern for the life of fishes in lakes, oceans, and rivers. Fish needs dissolved oxygen to stay alive. If the temperature of their water habitat increases, the concentration of dissolved oxygen is reduced and the life of the fishes is at stake.3. PressureThe pressure on the surface of a solution has less effect on the solubility of solids and liquids but a great effect on the solubility of gases.Solubility Curve:A solubility curve is a measurement shown on a graph that is utilized to establish the mass of a given dissolved item like salt or sugar in 100ml of water. The substance that is that is dissolved in the water is called a solute. If a figure falls under the line on the graph, it denotes an unsaturated solution which has the capacity to take up more solute.Solubility curves permit a scientist to establish the amount of a solute that can dissolve in 100 grams of water at a specific temperature.The Graph below shows the Grams of solute per 100g of water against temperature (°C)A steeper slope shows the increased effect on solubility by temperature rise.Solid Solutes against Gas Solutes: As the temperature rises, the solubility of a solid rises and solubility of gases decrease.A sample question:1. What is the quantity of sodium chloride that can be dissolved in 100 mL of water at 30°C?2. At 20°C, the highest amount of potassium chlorate is dissolved in 100 g of water. When the temperature is increased to 50°C, how much more potassium chlorate can be dissolved in the water?The amount of potassium chloride that can be dissolved in 50 mL of water at 50°C can be estimated as followsApplication of solubility product principle in qualitative analysisThe concepts of solubility of product and the common effect of ion are greatly employed in the process of qualitative analysis to separate essential radicals or cations into various groups.Weak acids and weak bases ionise partially in water leading to an equilibrium situation being attained in their solutions. For instance, in the ionization of a weak base NH4OH shown below:The ionization constant for the base isQualitative analysisThe widespread effect of ion is usually employed in qualitative analysis.The cations of group II elements (Hg2+, Pb2+, Bi3+, Cu2+, As3+, Sb3+, Sn2+) are normally precipitated as their sulphides for example the CuS and PbS through the passage of H2S gas in the presence hydrochloric acid which possesses the common H+ ions.The cations of group III elements are precipitated in their hydroxides forms by NH4OH in the presence of NH 4 Cl.The cations of group V are precipitated in their carbonates forms through the addition of (NH 4 ) 2 CO 3 , in the presence of HCl.In relation to solubility, salts can be classified into three main types:1. Soluble salts ie salts with their solubility greater than 0.1 M2. Slightly soluble salts that is salts with solubility in the range of 0.01 M and 0.1 M3. Sparingly soluble salt ie salts with solubility less than 0.01 MCrystallizationCrystallization is a procedure which chemists employ to purify solid compounds. It is one of the essential procedures every chemist ought to master to become capable in the laboratory. Crystallization is based on the principles of solubility.The difference between crystallization and solubilitySolubility is the capability to dissolve in a solvent. It is measured in units g per 100mL of solvent. Crystallization is the process through which crystals are formed. This could be from a molten substance but is normally from a solvent. As the solvent evaporatesSolutionA solution is a homogenous mixture of two or more substances.There are two components of a solution-Solute and solventSolution = solute + solventSoluteA solute is the constituent of a solution that is in little quantity.SolventA solvent is the constituent of solution that is in greater quantity.Saturated solution-Is a solution that can hold no more of the solute at a specific temperature.An Unsaturated solution-An unsaturated solution is a solution, which contains less amount of solute than is required to saturate it at that temperature.A super saturated solution-Is a solution that is more concentrated than a saturated solution. When an extra crystal of solute is added to the solution, the surplus solute forms crystal.An aqueous solution-Is a solution of any substance in which the solvent is water.

What Is KinematicI

Kinematics in physics

 

  Energy and Energy ChangesChemical changes occur on the molecular level. A chemical change results in the formation of a new substance.Examples of Chemical Changes include:• Combustion or burning e.g. burning wood• Dissolution of salt in water• combination of acid and base• digestion of food• cooking of an egg,• rusting of an iron or metal object• Combination of hydrochloric acid and sodium hydroxide to produce salt and water.Physical ChangesPhysical changes deals with energy and states of matter. A physical change unlike the chemical change does not lead to the formation of a fresh substance. Changes in state such as melting, freezing, vaporization, condensation, sublimation are all physical changes.Examples of physical changes include:• crumpling a sheet of paper• melting an ice cube• casting silver in a mold• breaking a bottle• Crushing a can.How to know a Chemical Change and a physical changeA chemical change results to the formation of a substance which was not there previously. You may be able to ascertain a chemical change through some indicators like light, heat, color alteration, gas formation, odor, or sound. The reactant and the product of a physical change are the same, although they may appear to be variable.A physical change may have occurred if the changes that are associated with a chemical change are not found. It can be hard to tell this in some reactions such as when sugar is dissolved in water. In this case the content is still the same chemically although the sugar has dissolved. The sugar is now present in the mixture as molecules of sucrose .Nevertheless, when you dissolve salt in water, the salt dissociates into its ions of Na+ and Cl- resulting to a chemical change. In the two scenarios, a white solid (salt) is dissolved into a clear liquid and in the two scenarios the reactant can be recovered by taking away the water. Irrespective of this, the two reactions are different.Endothermic and Exothermic ReactionsScores of chemical reactions discharge energy in the form of heat, light, or sound. These types of reactions are termed exothermic reactions. Exothermic reactions may occur instinctively and lead to an increased randomness or entropy (ΔS > 0) of the reacting system. They are designated by a negative heat flow meaning that heat is expelled to the surroundings and decrease in enthalpy (ΔH < 0). Exothermic reactions generate heat and may be explosive when performed in the lab.The second group of chemical reaction rather than give out heat to the surroundings absorbs heat from the surrounding in order to occur. These types of chemical reactions are referred to as endothermic reactions. Endothermic reactions are not spontaneous reactions. Work must be performed to be able to cause the reaction to take place. When endothermic reactions take up energy, a drop in temperature is calculated and noted on the course of the reaction. Endothermic reactions are denoted by positive heat flow and a rise in enthalpy (+ΔH).Examples of Endothermic and Exothermic ProcessesPhotosynthesis is one example of an endothermic chemical reaction. During photosynthesis, plants make use of the energy obtained from the sun in the conversion of carbon dioxide and water into glucose and oxygen. The process of photosynthesis takes up 15MJ of energy (sunlight) in order to produce one kilogram of glucose as exemplified in the equation below:Sunlight + 6CO 2 (g) + H 2 O(l) = C 6 H 12 O 6 (aq) + 6O 2 (g)One example of an exothermic reaction is the reaction between sodium and chlorine to form table salt. The formation of the table salt reaction gives off 411 kJ of energy for one mole of salt formed as exemplified below:Na(s) + 0.5Cl 2 (s) = NaCl(s)Exothermic- The term exothermic explains the process that gives out energy in the form of heat.Formation of a chemical bond usually leads to the release of an energy to the surrounding and can therefore be termed an exothermic process. Exothermic reactions frequently feel hot due to the fact that it is releasing energy to the surrounding.Endothermic – is used to denote a process or reaction that absorbs energy in the form of heat before it could occur.Breaking a chemical bond needs energy and is consequently regarded as Endothermic. Endothermic reactions frequently feel cold because they absorb heat from the surrounding.Examples of exothermic Processes Examples of endothermic Processes• freezing of water• solidification of solid salts• condensation of water vapor• formation of a hydrate from an anhydrous salt• formation of an anion from an atom in gaseous state• Total destruction of matter E=mc 2• division of an atom• melting of ice cubes• melting of solid salts• evaporation of liquid water• production of an anhydrous salt from a hydrate• producing a cation from an atom in the gaseous state• breaking up of a gas molecule• separation of ion pairs• boiling of an egg• baking of breadExamples of Exothermic Reactions Examples of Endothermic Reactions• burning of hydrogen• liquefaction of lithium chloride in water• combustion of propane• drying out the moisture of sugar with sulfuric acid• thermite• disintegration of hydrogen peroxide• disintegration of ammonium dichromate• halogenation of acetylene• Reaction of barium hydroxide octahydrate crystals with dry ammonium chloride• melting ammonium chloride in water• reacting thionyl chloride (SOCl 2 ) with cobalt(II) sulfate heptahydrate• mixture of water and ammonium nitrate• mixture of water and potassium chloride• reaction between ethanoic acid and sodium carbonate• Photosynthesis (chlorophyll is used in the reaction of carbon dioxide, water and energy to produce glucose and oxygen.Energy-level profile diagramsAn energy diagram can be employed to demonstrate the energy movements in these reactions and temperature can be made use of to evaluate them visibly.Every chemical process is characterized by changes in the energy. Before a reaction could occur it can either release or absorb energy. Exothermic reactions usually occur spontaneously and make their surroundings to heat up. That is the entropy or disorder of the environment is increased.The energy state of any chemical reaction can be denoted by Gibbs free energy.The EnthalpyEnthalpy is described in thermodynamics as an evaluation of the heat content of a chemical or physical system. Enthalpy (H) is an estimation of the total energy of a system and regularly denotes and demonstrates in a simpler way energy transfer between the reacting systems. A positive change in enthalpy denotes an endothermic reaction for the reason that energy is absorbed. A negative change in enthalpy denotes an exothermic reaction for the fact that the system has lost some energy to the environment.The EntropyA thermodynamic property that is the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work.The Free energyThe free energy of a reacting system is the difference between the internal energy of a system and the product of its entropy and absolute temperature.Gibbs free energyThe difference between the enthalpy of a system and the product of its entropy plus absolute temperature is referred to as Gibbs free energy. It is a determination of the useful work obtained from a thermodynamic system at constant temperature and pressure.HeatHeat is defined as the energy transferred from one system to another by thermal interaction.Law of conservation of energy:The law of the conservation of energy states that energy can neither be destroyed nor created but can be altered from one form to another. The total energy of a reacting system and the surroundings remains constant or unchanged.Change in Enthalpy is the expression that is used to explain the energy swap over that occurs with the surroundings at a constant pressure. It is denoted with the symbol ΔH.Enthalpy is the total energy content of the reactants. It is denoted with the symbol, H.ΔH = ΔH products - ΔH reactantsThe units of enthalpy are kilojoules per mole (kJmol -1 )An exothermic enthalpy change is constantly represented with a negative value, due to the fact that energy is expelled to the surroundings.ΔH = -xkJmol -1An endothermic enthalpy change is constantly represented with a positive value, since the energy is absorbed by the system from the surroundings.ΔH = + ykJmol -1 .Standard enthalpy changes: standard conditionsWhen we want to place the enthalpy changes of different types of reactions side by side each other for comparison, we must make use of standard conditions like known temperatures, pressures, amounts and concentrations of reactants or products.The standard conditions are listed below:• A pressure of 100 kilopascals (102kPa)• A temperature of 298K (25 oC )• Reactants and products in physical states, typical for conditions above.• A concentration of 1.0mol dm -3 for solutions.The o sign is used to denote a standard condition.Standard enthalpy change of reactionΔHorThe standard enthalpy change of reaction is the enthalpy change of that reaction when the amounts of reactants shown in the equation for the reaction, react under standard conditions to form the products in their standard states.Standard enthalpy change of formationΔHofThe standard enthalpy change of formation is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions. This means that both compound and elements are in their standard states.The Standard enthalpy change of combustionΔH ocThe standard enthalpy change of combustion is the enthalpy change when one mole of an element or compound is completely reacted with oxygen under standard conditions.The Energy Content of FuelsEnergy content is a significant property of both food and matter that is made use of during the process of heating. The energy that our body utilizes for day to day activities like sleep, walk, talk etc comes from the food that we eat, for instance the candy bar. The energy that is generated a fuel is burned is a crucial quantity, and we’d like to be capable of measuring the effectiveness of fuel.The energy content is the amount of heat produced by the combustion of 1 gram of a substance and is measured in joules per gram (J/g). Heat is a form of energy or in reality a flow of energy flow and it is usually calculated in calories.1 cal = 4.186 J.Every now and then it is tricky to accurately measure the amount of heat that is produced by a substance. The measurement is made easier by burning a particular quantity of the fuel to heat up water. The energy expelled by the fuel can then be estimated by calculating the heat absorbed by the water as calculated by the change in temperature of the water. Heat gained by water can be denoted byQ = change T * m * cwhereT is the temperature change, m is the mass, and c is the specific heat capacity constant of water.A brief summary of energy flow through the bodyFood that we ingest contains energy. The maximum amount of energy contained in the food we eat is a measure of the heat that is released after a total combustion of the food to carbon dioxide (CO2) and water in a bomb calorimeter. This energy is termed ingested energy (IE) or gross energy (GE).

 

 

 

 

 

chemical bonding

Chemical BondingThere are numerous types of chemical bonds and forces acting jointly to combine molecules together. The two most fundamental types of bonds are ionic and covalent bond. In ionic bonding, atoms transfer electrons to each other. Ionic bonds need at least one electron donor and one electron acceptor. On the contrary, atoms that have similar electro negativity share electrons through covalent bonds as for such atoms, donating or receiving electrons are not favorable.Chemical bonding is a means through which atoms unite to form molecules. Chemical bond exists between two atoms or groups of atoms when the forces acting between them are physically powerful enough to result to the formation of an aggregate with adequate stability to be termed an autonomous species. The no of bonds an atom forms matches up to the number of electron at its outer shell. Bond energy is the quantity of energy necessary to break a bond and create neutral atoms. In line with Coulomb’s law every bond as a result of attraction that exist between unlike charges. On the other hand, the manner this force is manifested varies depending on the atoms concerned. The main types of chemical bond are the ionic, covalent, metallic, and hydrogen bonds. The ionic and covalent bonds are ideal forms but the majority of the bond types are of an intermediary type.Bonding energy between two atomsThe interaction energy between two atoms at equilibrium is referred to as the bonding energy between the two atoms. To break the bond, this energy must be supplied from outside. Breaking the bond means that the two atoms become infinitely separated. In real substances that are made up of varieties of atoms, bonding is calculated by stating the bonding energy of the entire substances in terms of the disjointing distances among all atoms. There are different types of bonding:• Primary bonding: Ionic (involves transfer of outermost electrons)• Covalent (involves sharing of outermost electrons, directional)• Metallic (involves delocalization of valence electrons)• Secondary or van der Waals Bonding: (widespread, but less strong than primary bonding)• Dipole-dipole• H-bonds• Polar molecule-induced dipole• Variable dipole (the most weak bond)The Ionic BondingIonic bonding is the total transfer of outermost electron(s) between atoms. It is the type of chemical bond that produces two oppositely charged ions. In ionic bonds, the metal loses electrons to turn into a positively charged cation, while the non-metal receives those electrons to turn into a negatively charged anion. For ionic bond to occur there must be an electron donor, metal, and an electron acceptor, non metal.Ionic Bonding is occurs because metals have a small number of electrons in their outmost orbital. Through the loss of those electrons, these metals can attain noble-gas configuration and meet the octet rule. Likewise, non metals that have nearly 8 electrons in their outermost shell have the tendency of readily accepting electrons to attain their noble gas configuration. In ionic bonding, over 1 electron can be donated or received to fulfill the octet rule. The charge on the anion and cation matches up with the number of electrons contributed or received. In ionic bonds, the net charge of the compound must be zero.The ionic bond is a chemical bond formed as a result of attraction between two opposite charged ions. The atoms of metallic elements like sodium easily lose their valence electrons, whereas the atoms of non-metals like chlorine have the tendency to gain electrons. The reaction between them results to a highly stable ions which maintain their individual structures while approaching one another to form a stable molecule or crystal. In an ionic crystals such as sodium chloride, no separate diatomic molecules are present; instead, the crystal is made up of composed of independent Na+ and Cl− ions, with each being attracted to adjoining ions of the opposite charge giving rise to one single gigantic molecule.The covalent bondThe covalent bond is the type of bond formed when two atoms share a pair of electrons. There is no net charge on each of the atoms; the attractive force between them is formed through the interaction of the pair of electron within the nuclei of both atoms. When the interacting atoms share more than two electrons, it leads to the creation of double and triple bonds. This is because every shared pair forms its own particular bond. The interacting atoms, by sharing their electrons are able to attain a highly stable electron configuration that correspond to that an inert gas.Covalent BondingCovalent bonding is the chemical bond that results from sharing of electrons between atoms. This type of bonding arises between two atoms of the identical element or elements that are placed close to each other in the periodic table. Covalent bonding occurs mainly between non metals; but it can as well be found between non metals and metals alike.Polar and non-polar physical properties of covalent compoundsPhysical Covalent compounds propertiesStates (at room Solid, liquid, gas temperature)Electrical Usually none conductivityElectrical Usually none conductivity Varies, but usuallyBoiling point lower than ionic and Melting compounds Varies, but usuallySolubility in lower than ionic water compoundsIf we take methane (CH 4 ), as an example; in methane, carbon shares one electron pair with each of the 4 hydrogen atom; so that the total number of electrons shared by carbon is eight, which matches up with the numbers of electron in the valence shell of neon; every hydrogen atom shares two electrons, which matches up with the electron configuration of helium.In the majority of covalent bonds, every one of the atom contribute just a single electron to the shared pair. In some instances however, the two electrons are donated from the same atom. When this happens, it gives rise to a partially ionic character giving rise to what is called a coordinate link. In actual fact, a purely covalent bond can only be found among two identical atoms.Covalent bonds play a significant role in organic chemistry due to the capability of the carbon atom to form 4 covalent bonds. These bonds are arranged in specific directions in space, resulting to the complex geometry of organic molecules. If every one of the four bonds is one just like in methane, the resulting molecule will have the shape of a tetrahedron. The significance of shared electron pairs was originally discovered by theAmerican chemist G. N. Lewis (1916), who stated that there are only extremely few stable molecules that exist which have a total numbers of electrons that is odd. His octet rule permits chemists to forecast the most likely bond structure and charge allocation for molecules and ions. With the initiation of quantum mechanics, it was recognized that the electrons in a shared pair must possess opposite spin, as required by the Pauli Exclusion Principle.The molecular orbital theoryThe molecular orbital theory was developed to foretell the accurate sharing of the electron density in a variety of molecular structures. The American chemist Linus Pauling initiated the concept of resonance to clarify how stability is achieved when above one practical molecular structure is achievable: the actual molecule is a coherent mixture of the two structures.Metallic and hydrogen bondContrary to ionic and covalent bonds, which are copiously available in a great number of molecules, the metallic and hydrogen bonds are highly specific.The metallic bond is the bond accountable for the crystalline structure of pure metals. This bond cannot be ionic due to the fact that every one of its atoms is identical. It cannot also be covalent ordinarily due to the fact that there are very few valence pairs of electrons to be shared among adjoining atoms. As an alternative, the valence electrons are shared jointly by all the atoms in the crystal. The electrons act as a free gas moving within the lattice of preset, positive ionic cores. The intense mobility of the electrons in a metal gives explanations for its high thermal and electrical conductivity.Hydrogen bonding is a very powerful electrostatic attraction between two independent polar molecules. That is between the molecules in which the charges are unequally dispersed, characteristically containing nitrogen, oxygen, or fluorine. These elements have physically powerful electron-attracting power, and the hydrogen atom serves as an overpass between them. The hydrogen bond, which plays a crucial role in molecular biology, is by far weaker than the ionic or covalent bonds. Hydrogen bond is answerable for the structure of ice.Bonding in Organic ChemistryIonic and Covalent bonds are the two top limits of bonding. Polar covalent is the midway type of bonding in between the two extremes. Some ionic bonds possess covalent character and some covalent bonds are partly ionic. For instance, the majority of carbon-based compounds are covalently bonded, however they can also be partly ionic.Polarity is an evaluation of the separation of charge in a compound. A compound's polarity is reliant on the symmetry of the compound together with the differences in electronegativity between atoms. Polarity arises when the electron pushing elements from the left side of the periodic table, shares electrons with the electron-pulling-elements from the right side of the period table. This generates a spectrum of polarity, with ionic (polar) at one end, covalent (non-polar) at the other end, and polar covalent in the center.In co-operation, these bonds are vital in Organic Chemistry. Ionic bonds are significant because they allow the synthesis of specific organic compounds. Covalent bonds are particularly essential since most carbon molecules interact primarily through covalent bonding. Covalent bonding permits molecules to share electrons with other molecules, forming long chains of compounds and giving rise to more complexity in life.Polar and Non-Polar ShapesMolecules that have a linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral shape, are non-polar in nature. These are shapes which do not have non-bonding lone pairs like Methane, CH4. However if a few bonds are polar while the rest are not, there will be a general dipole, and the molecule will be polar. Example Chloroform, CHCl3.Dipole-Dipole BondsWhen two polar molecules come close to each other, they will position themselves in order to let the negative and positive sides’ line up. There will be an attractive force linking the two molecules together, but it is not virtually as well-built a force as the intramolecular bonds. This explains the way different types of molecules bond together to form bulky solids or liquids.Van der Waals forces are initiated by temporary dipoles formed when electron locations are asymmetrical. The electrons are continually tracking the nucleus, and by chance they could come very close together. The uneven concentration of electrons could result to one side of the atom becoming more negatively-charged than the other, forming a temporary dipole. Van der Waals forces are the reason why nitrogen can be liquified.