P~9a~~ PHYSICAL CHEMISTRY Dr J.N Gurtu Dr H.C Khera M.Sc., Ph.D M.Sc., Ph.D Former Principal Reader & Head, Deptt of Chemistry, Meerut College, Meerut loP College, Bulandshahr » PRAGATI PRAKASHAN © Authors-Physical Chemistry Vol I PRAGATI PRAKASHAN Head Office: Educational Publishers PRAGATI BHAWAN 240, W K Road, Meerut-250 001 SMS/Ph : (0121) 6544642, 6451644 Tele/Fax: (0121) 2640642, 2643636 Visit us at : www.pragatiprakashan.in e-mail: pragatiprakashan@gmail.com Regd Office: New Market, Begum Bridge, Meerut-250 001 Edition 2010 ISBN-978-81-8398-496-6 Published by : K.K Mittal for Pragati Prakashan, Laser Typesetting : Pragati Laser Type Setters Pvt Ltd., (Phone: 2661657) Meerut Printed at: Arihant Electric Presss, Meerut CONTENTS IIUlij' MATHEMATICAL CONCEPTS AND COMPUTER Logarithmic and Antilogarithmic Relations Find out the values of the following Differentiation with Examples Numerical Problems Integration and give important formulae Numerical Problems Terms Permutation and Combination with Examples 24-41 Numerical Problems 42 Probability Definition 43-50 Numerical Problems 51 Logarithmic, Trigonometric Series 52 Maxima and Minima 53-57 Numerical Problem 58 Functioning, Characteristics, Limitations Computer Programing Flow Charts Fortan, Cobol, Basic, Pascal Operating System Exercise Multiple Choice Questions Fill in the Blanks True or False 4-12 13 14-23 24 1-55 11-13 13 16 22 23 29 32 32 33 34 38 49 50 51 52 52 54 54 o o o 111~lij" GASEOUS STATE 5~102 Nature of R and its value in different units 56 Short account of kinetic theory of gases and derivation of kinetic equation 57 (a) 59 Short account of kinetic theory of gases Derivation of PV = RT and show how the various gas laws are consistent with it? (b) Expression for kinetic energy of one mole of gas Values of Cv and Cp from kinetic equation and variation of CplCv with molecular complexity of the gas 62 (viii) Distribution of molecular velocities of Maxwell's law 65 (a) Average velocity, root me~n square velocity and most 67 probable velocity and relation among them (b) Calculation of RMS velocity from kinetic theory of gases 67 Kinetic equation of gases 68 Ideal gas and its difference with a real gas 70 (a) Limitations of PV = RT and improvements suggested by 70 vander Waals Derivation of vander Waals equation (b) Units of vander Waals constants 70 (c) Show that effective volume of gas molecules is four 70 times greater than actual volume of molecules 10 (a) Critical phenomenon, calculation and determination of 75 critical constants, short note on continuity of state 79 11 Some short questions on vander Waals equation 81 12 Short notes on : (a) Various equation of state (b) Law of corresponding states (c) Mean free path (d) Critical phenomenon and its utility (e) Collision frequency (0 Law of equipartition of energy (g) Specific heat ratio (h) Boyle temperature (i) Continuity of state 13 Methods for producing cold and liquefaction of gases, 86 inversion temperature o Numerical Problems 98 o Multiple Choice Questions 100 o Fill in the Blanks 101 o True or False 102 IIn"j'" CHEMICAL AND PHASE EQUILmRIUM Chemical Equilibrium I I 103-171 Law of mass action and eqUilibrium constant 103 Short notes on the following : (i) Work function (ii) Free energy Thermodynamic derivation of law of mass action 104 108 Thermodynamic derivation of van't Hoff isotherm Thermodynamlc··-derivation of van't Hoff isochore or van't Hoff equation Thermodynamic derivation of Clapeyron equation and Clausius-Clapeyron equation Le-Chatelier-Braun principle and applications to different equilibria o Numerical Problems 109 111 Explanation and illustration of phase, component and degree of freedom Phase rule and its thermodynamic derivation Explain: Can all four phases in a one component system co-exist in equilibrium? Application of phase rule to water system Application of phase rule to sulphur system Short notes on : (a) Non-variant system in phase rule studies (b) Triple point (c) Transition point Two component system, graphical representation, reduced phase rule equation, condensed state Application of phase rule to lead-silver system Application of phase rul~ to potassium iodide and water system Determination of number of phases and components of different systems Calculation of degree of freedom Determination of number of phases, components and degree of freedom of different systems Ideal solutions, vapour pressure of such solutions Non-ideal or real solutions, vapour pressure curves of completely miscible binary solutions Theory of fractional distillation of binary solutions (a) Theory of partially miscible liquid pairs, e.g., (i) Phenol-water system Oi) Triethyl-amine water system 126 IPhase Equilibrium I 10 11 12 13 14 15 16 114 118 122 -129 131 131 134 137 138 140 142 143 143 144 144 147 150 154 (x) (b) (iii) Nicotine-water system Influence of impurities on critical solution temperature 154 IDistribution Law I Nemst's distribution law limitations applications 157 Nemst's distribution law modification when the solute 162 undergoes dissociation or association Numerical Problems 163 o Multiple Choice Questions 169 Fill in the Blanks 170 True or False 170 o o o COLLOIDAL STATE 172-210 Explain the terms : colloidal state and colloidal solution, 172 methods for preparation and purification of colloidal solutions (a) Difference between true solution colloidal solution and 177 suspension (b) Types of colloidal systems 177 Preparation of colloidal solutions of AS2S3 Fe(OH)3 gold 178 sulphur silicic acid carbon mastic iodine Short notes on : 180 (i) Lyophilic and lyophobic colloids (ii) Peptisation (iii) Dialysis (iv) Ultramicroscope (v) Tyndall effect (vi) Brownian motion (vii) Electrophoresis (viii) Electro-osmosis (ix) Coagulation (x) Hardy-Schulze law (xi) Protection (xii) Gold number (xiii) Stability of lyophilic colloids (xiv) Iso-electric point (xv) Emulsion (xvi) Gel (xvii)Electrical double layer or Zera potential (xi) (a) (b) Explain the following facts: 199 (a) A sulphur sol is coagulated by adding a little electrolyte, whereas a gelatin sol is apparently unaffected (b) What happens when a colloidal solution of gold is brought under the influence of electric field? (c) What happens when an electrolyte is added to colloidal solution of gold? (d) What happens when a beam of light is passed through a colloidal solution of gold? (e) A colloidal solution is stabilised by addition of gelatin (f) Presence of H2S is essential in AS2S3 sol though H2S ionises and should precipitate the sol (g) Why ferric chloride or alum is used for stoppage of bleeding? Applications of colloids in chemistry Sol-gel transformation Note on thixotropy Multiple Choice Questions Fill in the Blanks True or False Origin and significance of charge on a colloidal particle Classification of the sols: Gold, Fe(OH)3, gelatin, blood, sulphur, AS2S3 198 198 200 2C4 206 208 209 209 o o o III~I'M CHEMICAL KINETICS AND CATALYSIS Chemical Kinetics I I 211-276 (a) Explain the terms: rate of chemical reaction, velocity 211 coefficient, molecularity and order of reaction (b) Difference between molecularity and order of reaction (c) Why reactions of higher orders are rare? (d) Factors which affect reaction rates? Zero order reaction, rate expression, characteristics 215 Half order reaction, rate expression, characteristic 216 First order reaction, rate expression, characteristics, examples 217 (a) (b) Pseudo-unimolecular reactions Study of kinetics of hydrolysis of methyl acetate Half life period for a first order reaction 219 220 Second order reaction, rate expression, characteristics, examples and study of kinetics Half life period for a second order reaction Third order reaction, rate expressions, characteristics and examples 10 nth order reactions, rate equation and characteristic 11 Methods employed in determining the order of reaction 12 Energy of activation and temperature coefficient 13 Activation energy, potential energy barrier and Arrhenius law 14 Collision theory for unimolecular reactions 15 Mathematical treatment of transition state theory, comparison with collision theory Numerical Problems o 221 224 225 227 228 230 233 235 236 242 ICatalysis I Catalyst, catalysis, types and classification of catalysis 251 characteristics of catalytic reactions Notes on the following: 258 (a) Catalytic promoters (b) Catalytic poisons Theories of catalysis, industrial applications of catalysts 261 Enzyme catalysis, characteristics and examples of enzyme 265 catalysis, kinetics of enzyme catalysis Note on acid-base catalysis 269 Multiple Choiae Questions 270 Fill in the Blanks 274 True or False 275 o Log and Antilog Tables (i)-(iv) o o o MATHEMATICAL CONCEPTS AND COMPUTER MATHEMATICAL CONCEPTS Problem 1: Expillin the logarithmic and antilogarithmic reilltions with suitable examples [A] Index Multiplication of equal terms: then multiplication will be x n , i.e., If the term x is multIplIed Il tImes, x x x x x x x x n times = x" Here x is called the base and n is called index [8] Laws of Index m and ~ tn-II x" xo= (Xlll)" = Xlllll (xyt =x"l (xlyr = x"ly" d x -n =1 7.xn =-an -n n X xlln X = n{; X [C] Logarithms Definition: If ab = c; then exponent 'b' is called the logarithm of number 'c' to the base 'a' and is written as log c = b, e.g., J~ = 81 ~ logarithm of 81 to the base is 4, i.e., log3 81 = Note: a b = c, is called the exponential form and loga c = b is called the logarithmic form, i.e., T3 = 0.125 (i) (Exponential form) (Logarithmic form) log2 0.125 =-3 (Logarithmic form) (ii) log64 ="2 (64)112 = (Exponential form) Laws of Logarithms [I] First Law (product law) : The logarithm of a product is equal to the slim of logarithms of its factors logo (m X 11) = log" III + log" /I 262 PHYSICAL CHEMISTRY-I (3) Fonnation of methyl benzene, C6H5CH3 by reaction between benzene (C6H6) and methyl chloride (CH3CI) using anhydrous aluminium chloride AICI 3, as catalyst (Friedel-Craft's reaction) AICI) C6H6 + CH3CI ~ C6H5CH3 + HCI Mechanism: CH3CI + AICI ~ [CH3 [AICI4 f t Intermediate compound C6~ + [CH3t [AICI 4f ~ C6HSCH3 + AICI + HCI (4) Thermal decomposition of potassium chlorate (KCI0 3) in the presence of manganese dioxide (Mn02)' MnO, 2KCI03 ~ 2KCI + 302 Mechanism: 2KCI0 + 6MnOz ~ 6Mn03 + 2KCI Intermediate compound 6Mn03 ~ 6MnOz + 30 It may be noted that the actual isolation of intermediate compounds which would prove their existence is very difficult As already stated, by their very nature they are upstable In general, the intermediate compounds suggested as being formed are usually possible rather than proved Adsorption Theory or Modem Theory of Heterogeneous Catalysis Adsorption theory explains the mechanism of a reaction between two gases catalysed by a solid (heterogeneous or contact catalysis) According to this theory, the catalyst acts by adsorption of the reacting molecules on its surface Generally speaking, four steps can be put forward for heterogeneous catalysis For example, for the following reaction, Catalyst A(g) + B(g) ~ C(g) + D(g) the steps are as follows : Step Adsorption of reactant molecules The reactant molecules A and B strike the catalyst surface They are held up at the surface by weak vander Waals forces (physical adsorption) or by partial chemical bonds (cllemisorptioll) Step Formation of activated complex The particles of the reactants adjacent to one another JOIn to form an intermediate complex (A - B) The activated complex is unstable It has only a fleeting existence Step Decomposition of activated complex 'The activated complex breaks to form the products C and D The separated particles of the products are held to the catalyst surface by partial chemical bonds 263 CHEMICAL KINETICS & CATALYSIS Step Desorption of products The particles of the products are desorbed or released from the surface They are stable and can lead to an independent existence r··'·······'·N , " ' :~; ''''~;;;''''''''''''''''''".S2,,'' Catalyst """""''' """ """"''''' ;;;~; """"""""~"'''''''''''''' Catalyst " """'''''''''''''''''''''''''''''''''''''''''', !!;,t;i;;;i·;;~;:;?~~;.·~~~~~~?~~;:::~t··g::.····.· The mechanism of contact catalysis may vary in details, depending on the nature of the reactants Consider the example of hydrogenation of ethene in presence of nickel In this casse, ethene adds hydrogen in the presence of nickel as a catalyst to yield ethane H _N_i :(c_a_ta ;ly'-st-'-)~) H Ethene gas H I I H-C C-H I I H Ethane (gas) The catalyst functions according to the following steps Step Adsorption of hydrogen molecules Hydrogen molecules are adsorbed on the nickel surface due to the residual valence bonds of the nickel atoms Step H-H bonds are broken The H-H bond is smaller (0.74 A) than Ni-Ni bond Therefore, the H-H bond of the adsorbed hydrogen molecule is stretched and weakened The weakened bond breaks, separating the hydrogen atoms The separated hydrogen atoms are held to the nickel surface by chemical bonds Step Formation of the activated complex The chemisorbed hydrogen atoms then attach to ethene molecule by partial chemical bonds Therefore, unstable activated complex is formed Step Decomposition of the activated complex and desorption of ethane molecule The unstable activated complex decomposes to form ethane molecule The freed catalyst surface is again available for further action 264 PHYSICAL CHEMISTRY-I il'::"""'''''''''~'''''''''''''''''''''''''''''''''''''''''M""""""""'·":'~ :1 H,, Step /H H,, j H/r:I" H )~ :'.! Step Step 2;' H I I HH/C C" HH @ @ I Step \ :::.:\::\U\ '~i~: ~~ ;.~~~~~ ~~.~~~ ~;~~~~~~~~~~ ~~ j/:::;:i{::::U/!::::·: \u:=::nt} .~~~.e~e o.~ ~i.~~.~~.~~r:r~c~' I)/\/(I(U:: The adsorption theory explains the catalytic activity as follows: (1) Metals in a state of fine sub-division or colloidal form are rich in free valence bonds and hence they are more efficient catalysts than the metal in lumps (2) A promoter increases the valence bonds on the catalyst surface by changing the crystal lattice and thereby increasing the active centres (3) Catalytic poisoning occurs because the so-called poison blocks the free valence bonds on its surface by preferential adsorption or by chemical combination [II] Industrial Applications of Catalysts Tht" presence of a catalyst is very useful in many industrially important reactions, which are either very slow or take place at a very high temperature :.', .:.' ',' ,',::-::-:,:::::::::,:':':-:::':::':,:',.;::.:::,:,:;:;::::';::'';;';''':-:-':;:::';''::::''\:{ "" 265 CHEMICAL KINETICS & CATALYSIS Hence to decrease the cost of production it is essential to make use of a suitable catalyst A few important examples of heterogeneous catalytic reaction of industrial applications are given as follows: Catalyst and other favourable conditions Reaction Haber's process for the manufacture of Finely divided Fe + molybdenum (as ammonia promoter) 200 atm pressure and N2 + 3H2 ~ 2NH3 temperature.400°-450°C The manufacture of chlorine by Deacon's Cupric chloride + excess of air at a process temperature of 500°C 4HCI + 02 ~ 2H20 + 2Cl2 Ostwald's process for the manufacture of Platinised asbestos + excess of air (as HN0 promoter) and temp 300°C 4NH3 + 502 ~ 4NO + 6H20 2NO + 02 4N02 + 2H20 + 02 ~ ~ 2N02 4HN03 Manufacture of hydrogen by Bosch's Ferric oxide + Cr203 (as a promoter) at a process temp of 400°-600°C (CO + Hz) + H20 ~ C02 + H20 Manufacture of methyl alcohol from ZnO + Cr203 (as a promoter) 200 atms water gas pressure and temp of 450°C CO+H2 +H2 ~ CH30H Water gas Water gas Chamber process for the manufacture of H2S04 ZS02 + 02 + [NO] ~ 2S03 + [NO] S03 + H20 ~ H2S04 Acetic acid from acetaldehyde 2CH3CHO + 02 ~ 2CH3COOH Nitric oxide Problem What is biochemical or enzYme catalysis? Discuss the characteristics and some examples of enzYme catalysis Discuss the kinetics of enZJme catalysis Or Explain enZJme catalysed reactions (Meerut 2006, 2004) Biochemical or Enzyme Catalysis Enzymes are complex nitrogeneous organic compounds They are produced in the living cells of plants and animals On dissolving in water they form the colloidal solution hence they behave as very active catalysts in certain biochemical reactions and are known as biochemical catalysts and the phenomenon itself is known as biochemical catalysis [I] Characteristics of Enzyme Catalysts (1) Enzymes form a colloidal solution in water and hence they are very active catalysts 266 PHYSICAL CHEMISTRY-I (2) Like inorganic catalysts they cannot disturb the final state of equilibrium of a reversible reaction (3) They are highly specific in nature, i.e., one catalyst cannot catalyse more than one reaction (4) They are highly specific to temperature The optimum temperature of their activity is 35°C to 40°C They are deactivated at 70°C (5) Their activity is increased in the presence of certain substances, known as co-enzymes (6) A small quantity of enzyme catalyst is sufficient for a large change (7) They are destroyed by U.v rays (8) Their efficiency is decreased in presence of electrolytes [II] Examples of Enzyme Catalysis The following are some examples of biochemical or enzyme catalysis (1) Manufacture of ethyl alcohol from cane sugar Glucose Fructose Zymase ) 2C 2H50H + 2C0 C6H120 (2) Manufacture of acetic acid from ethyl alcohol C2H50H + O2 Mycoderma aceti ) C H3 CO H 0 + H2 (3) Conversion of starch into maltose 2(C~1005)n + nH20 Diastase ~ nC 12H220 II Starch Maltose C 12H220 U + H20 Maltase -~) 2C6H l2 Maltose Glucose (4) In the estimation of urea Urease enzyme completely converts urea into ammonium carbonate /,NH2 /' O=C",- + 2H20 Urease ~ (NH4hC0 "'- NH2 (5) In digestive tract (a) In stomach, pepsin enzyme converts proteins into peptides, whereas in intestines, pancreas trypsin converts proteins into amino acids by hydrolysis These amino acids are absorbed by blood and are used in the building of tissues (b) The enzyme ptyalin present in human saliva converts starch into glucose Ptyalin ) nC 6H l2 Gluco;e J 267 CHEMICAL KINETICS & CATALYSIS [III] Kinetics of Enzyme Catalysis or Michaelis-Menten Equation A reactant in an enzyme catalysed reaction is known as substrate According to the mechanism of enzyme catalysis, the enzyme combines with the substrate to form a complex, as suggested by Henri (1903) He also suggested that this complex remains in equilibrium with the enzyme and the substrate Later on in 1925, Briggs and Haldane showed that a steady state treatment could be easily applied to the kinetics of enzymes Some photochemical reactions and some enzymic reactions are reactions of the zero order With S representing substrate, E the enzyme, ES an enzyme-substrate complex and P the products, the mechanism of the enzyme catalysed reaction is presumed to be adequately represented by kj k E+S~ ES~E+P k2 where kl' k2' k3 are the rate constants for the respective reactions The rate of formation of the complex ES is, evidently given by the following equation, d[!S] = = kl [E] [S] - k2 [ES] - k3 [ES] (1) where [E], [S] and [ES] represent molar concentrations of the free enzyme, substrate and the complex, i.e., bound or reacted enzyme, respectively Now [E] cannot be experimentally measured The equilibruim between the free and bound enzyme is given by the enzyme conservation equation, i.e., [E]o = [E] + [ES] where [E]o refers to the total enzyme concentration So, [E] = [E]o - [ES] On substituting the value of [E] in equation (1), we get d ~S] = kl {[E]o - [ES]} [S] - (k'l + k3) [ES] =0 (2) As the reaction proceeds, the intermediate complex formed in accordance with the suggested mechanism, decomposes instantaneously according to the same mechanism On applying the steady state principle, we have d [ES] = dt 268 PHYSICAL CHEMISTRY-I At the stationary state, equation (2) may be written as, k\ {[E]o - [ES]} [S] = (k2 + k 3) [ES] or k\ [E]o [S] = {(k2 + k3) + k\ [S]} [ES] [ES] = = k\ [E]o [S] (k2 + k3) + kI [S] [E]o [S] k2 + k3 kI + [S] The rate of formation of the product, P, i.e., r is represented by the equation, r = d [P] dt =k3 [ES] (3) Substituting the value of [ES] in equation (3), we get d [P] k3 [E]o [S] r= = dt k2 + k3 k;-+[S] (k2 + k3) The quantIty k is known as Michaelis constant and may be denoted by Km Therefok, d [P] _ k3 [E]o [S] (4) dt - Km + [S] Equation (4) is known as Michaelis-Menten equation Further simplification of equation (4) can be made If it is assumed that all the enzyme has reacted with the substrate at high concentrations the reaction will be going on at maximum rate No free enzyme will remain so that [E]o = [ES] So, from equation (3), we get rrnax = Vrnax = k3 [E]o where "'max reters to maximum rate, using the notation of enzymology So, Michaelis-Menten equation can also be written as, Vmax [S] r= Km + [S] If r = Vma J2, i.e., if the rate of formation of product is equal to half of the maximum rate at which the reaction proceeds at high concentration of substrate, then Km = [S] Thus, Michaelis COli stant is equal to that concentration of substrate, S at which the rate of formation of the product is half the maximum rate obtained at a high cOllcentration of substrate CHEMICAL KINETICS & CATALYSIS 269 From equation (4), we can draw the following conclusions: (i) If [S] is very small as compared to Km, the factor Km/[S] will be very large as compared to unity and so the rate of formation of P, i.e., d [P]Idt will be directly proportional to [8] In other words, the reaction will be of the first order with respect to S (Fig 13) Maxlmum rate, Vmax Vmax [SJIKm (first order) Substrate concentration (S) _ (ii) If [S] is very large as compared to Km, the factor Km/[S] will be negligibly small as compared to unity and so the rate of formation of P, i.e., d [P]/dt will be independent of the concentration [S] In other words, the reaction will be of zero order with respect to S (Fig 13) (iii) If [S] is very small or very large, the reaction remains of the first order with respect to the total concentration, [E]o of the enzyme Problems mite a short note on acid-base catalysis (Meerut 2007) As a result of the work of Bronsted, Lowry and others, it has become evident in recent years that a variety of atomic, molecular and ionic species are capable of catalysing chemical reactions For some processes, hydrogen ions appear to be effective, while other reactions are catalysed by hydroxyl ions, cations of weak bases, anions of weak acids, undissociated molecules of acids and bases etc This general acid catalysis involves cases where all acids act as catalysts, while general base catalysis refers to processes catalysed by bases of all kinds In some cases, both acids and bases are effective, while in others a particular species is effective General acid-base catalysis is illustrated by mutarotation of glucose, which is catalysed by hydrogen, hydroxyl and complex ions, as well as by the acids and bases, though the most effective catalyst is the hydrogen ion 270 PHYSICAL CHEMISTRY-I Mechanism of acid-base catalysis: It is accepted that acid-base catalysis involves a reversible acid-base reaction between the substrate and catalyst This is in agreement with the protonic concept of acids and bases, since acid catalysis depends on the tendency of the acid to lose a proton, while base catalysis depends upon the tendency of the base to gain a proton The mechanism of reaction involving Wand OIr ion catalysis may be expressed as follows by taking the example of hydrolysis of esters (a) With W ions as catalyst ORO II I n+ R I I+ HO ' R I+ I CH,-C-O + n -> CH,-C-O -H -' -> CH,-C/\H H H (b) With OS- ions as catalyst ORO II I R I I I R I I I CH3-C-O + OIr ~ CH3-C-O+ ~ CH3-C-O+-H H-O H-O CH3COOH + ROH The rate of reaction is given by dx -d = kH+ C H+ Cester + kOH- C OH Cester + kH,o CH,o Cester t where kH+ and koH- are the catalytic coefficients of hydrogen and hydroxyl ions ~ MULTIPLE CHOICE QUESTIONS The dimension of first order rate constant is : (i) time-1 (ii) time (iii) time x conc (iv)time-l x conc- l The dimension of second order rate constant is : (i) times x conc (ii) time- l x conc- l (iii) time x conc-1 (iv) time-1 x conc-2 271 CHEMICAL KINETICS & CATALYSIS hydrolysis of methyl acetate by acid is of : Zero (ii) First order Second order (iv) Third order hydrolysis of ethyl acetate by NaOH is of : Zero (ii) First order Second order (iv) Third order reaction rate of a reaction 2A ~ 3B is given by : (a) _ d [A] (b) _! d [A] ~ ~ The (i) (iii) The (i) (iii) The (c) + ~ d ~~] (d) + d ~] For a reaction A + B ~ Products, the reaction rate is given by, : dx = k[A] [Br dt The order of reaction with respect to A and B are : (ii) 1, (iii)O (i) 1,0 (iv) 2, The half life period of a first order reaction is 20 The time required for the concentration of the reactant to change from 0.4 M to O.I,M is : (ii) 40 (iii) 60 (iv) 80 (i) 20 The ratio of the time required for 75% of a first on':,,! rr,ction to complete to that required for 50% of the reaction is : (i) 4: (ii) I : (iii)2: I ' (iv)3: The time required to decompose half of the reaction for a n'h order reaction is also doubled The order of reaction is : (ii) (iii) (iv) (i) 10 The minimum energy required for reactant molecules to enter into chemical 11 12 13 14 reaction is known as : (i) Kinetic energy (ii) Potential energy (iii) Activation energy (iv) Threshold energy A first order reaction is 75% completed in 32 minutes For 50% completion, it will take: : (i) (ii) (iv) 32 (iii) 16 The elementary step of the reaction 2Na + Cl ~ 2NaCI is found to follow third order reaction kinetics The molecularity of the reaction is : (i) (ii) (iii) (iv) In a reaction A ~ B, the reaction rate is doubled on increasing the concentrations of reactants four times The order of reaction is : (i) 0, (ii) (iii) (iv) On plotting loglok against Iff, the slope of the straight line is given by:: (1) Ea R " (n) E (iii) 2.30; R Ea -R 272 15 16 17 18 19 20 21 PHYSICAL CHEMISTRY-I If the plot of 10glO [A] against time is a straight line with a negative slope, the order of reaction is : (ii) (iii) (iv) (i) In the hydrogenation of oils the catalyst used is : (i) Iron (ii) Platinum (iii) Nickel (iv) Molybdenum The effect of a catalyst in a chemical reaction is to change the: (i) Activation energy (ii) Equilibrium concentration (iv) Final product (iii) Heat of reaction The catalyst used in the contact process of sulphuric acid manufacture is : (i) Oxides of nitrogen (ii) Nickel (iii) Vanadium pentoxide (iv) Manganese dioxide Which of the following is used as a contact catalyst? (i) Boron (ii) Germanium (iii) Nickel (iv) U~anium Which of the following statements is universally correct? (i) A catalyst remains unchanged at the end of the reaction (ii) A catalyst physically changes at the end of the reaction (iii) A catalyst takes part in the chemical reaction (iv) A catalyst can induce chemical reaction The catalyst used for the oxidation of ammonia to nitric acid is : (i) Cupric chloride (ii) Iron oxide (iii) Platinum (iv) Manganese dioxide 22 A substance that regards the rate of chemical reaction in the presence of a catalyst 23 24 25 26 27 is called : (i) An inhibitor (ii) A positive catalyst (iii) An auto-catalyst (iv)A promoter A catalyst poison is essentially: (i) A homogeneous catalyst (ii) A heterogeneous catalyst (iii) An inhibitor (iv) An auto-catalyst Catalyst poisons (temporary poisoning) act by : (i) Chemically combining with the catalyst (ii) Getting adsorbed on the active centres on the catalyst surface (iii) Chemical combination with anyone of the reactants (iv) Coagulating the catalyst Which of the following types of the metal make the most effiCIent catalyst? (i) Transition metals (ii) Alkali metals (iii) Alkaline earth metals (iv) Coloured metals Which one of the following statements is incorrect? (i) Presence of a catalyst does not alter the equilibrium concentration in a reversible reaction (ii) Change of temperature alter the rate of catalysed reaction in the same proportion as of the reaction without catalyst (iii) Homogeneous catalysis depends upon the nature and extent of the surface (iv) Change of a catalyst may change the nature of the reaction Enzymes are: (i) Micro-organisms (ii) Proteins (iii) Inorganic compounds (iv) Moulds CHEMICAL KINETICS & CATALYSIS 28 ' 1; 273 A pho~chemical reaction is : (i) Catalysed by light (ii) Initiated by light (iii) Accompanied with emission of light (iv) Accompained with absorption of light Platinised asbestors is used as catalyst in the manufacture of H2S04, It is an example of : (i) Homogeneous catalyst (ii) Auto-catalyst (iii) Heterogeneous catalyst (iv) Induced catalyst 30 The enzyme ptyalin used for digestion of food is present in : (ii) Blood (i) Saliva (iii) Intestine (iv) Adrenal gland 31 A catalyst is a substance with : (i) Increase the equilibrium concentration of the product (ii) Change the equilibrium constant of the reaction (iii) Shortens th time to each equilibrium (iv) Supplies energy of the reaction 32 An example of auto-catalytic reaction is : (i) The decomposition of nitroglycerine (ii) Thermal decomposition of KCl0 3• Mn02 mixture 29 ~ (iii) Break down of 14C6 33 34 3? 36 37 38 (iv) Hydrogenation of vegetable oil using nickel catalyst The efficiency of an enzyme in catalysing a reaction is due to its capacity: (i) To form a strong enzyme-substrate complex (ii) To decrease the bond energies in the substrate molecule (iii) To change the shape of the substrate molecule (iv) To lower the activation energy of the reaction A catalyst: (i) Increases the energy change in a reaction (ll) Increases the free energy change in a reaction (iii) Neither decreases nor increases the free energy change in a reaction (iv) Can increase or decrease the free energy change in a reaction but it depends on the catalyst Starch is converted into disaccharide in the presence of : (i) Diastase (ii) Maltase (iii) Lactase (iv)Zymase Glucose or fructose is converted into C2H50H in the presence of : (i) Invertase (ii) Maltase (iii) Zymase (iv) Diastase A ~talyst increases the rate of a chemical reaction by : (i) Increasing the activation energy (ii) Decreasing the activation energy (iii) Reacting with reactants (iv) Reacting with products Which of the following statement is correct? (i) Enzymes are in colloidal state (ii) Enzymes are catalysts (iii) Enzymes catalyse any reaction (iv) Urease in an enzyme 274 39 40 41 42 43 44 45 46 47 48 49 PHYSICAL CHEMISTRY-I A catalyst is used: (i) To vaporise the compound (ii) To kill the enzyme (iv) To balance the reaction (iii) To alter the velocity of reaction Enzymes Il.re : (i) Substances made by chemists to activate washing powder (ii) Very active vegetable catalysts (iii) Catalysts found in organisms (iv) Synthetic catalysts Which of the following catalysts is used for preparing toluene by reacting benzene with CH 3Cl? (i) Ni (ii) Anhydrous AlCl (iii) Pd (iv) Pt The rusting of iron is catalysed by which of the following? (i) Fe (ii) O2 (iii) Zn (iv) H+ In which of the commerical process, a catalyst is not used? (i) Haber's process (ii) Deacon's process (iii) Solvay process (iv) Lead chamber process Which of the following statements is correct for a catalyst? (ii) It alters the rate of the reaction (i) It supplies energy to the system (iii) It alters the equilibrium constant (iv) It is used up in the reaction Organic catalysts differ from inorganic catalysts in : (i) By acting at very high temperature (ii) By acting at low temperature (iii) Being used up (iv) Being proteneous in nature Which one of the following statements regarding catalyst is not true? (i) A catalyst can initiate a reaction (ii) A catalyst remains unchanged at the end of the reaction (iii) A catalyst does not alter the equilibrium in a reversible reaction (iv) Catalysts are sometimes very specific in terms of reactions Which statement is incorrect for heterogeneous catalysis? (i) Catalyst is absorbed on the surface (ii) Active centres are found on the surface of catalyst (iii) Catalyst increases the energy of activation (iv) None of these Which of the following is used as a contact catalyst? Oi) Nickel (i) Boron (iii) Germanium (iv) Uranium Which one of the following statements is incorrect in the case of heterogeneous catalyst? (i) The catalyst lowers the energy of activation (ii) The catalyst actually forms a compound with the reactant (iii) The surface of the catalyst plays a very important role (iv) There is no change in the energy of activation Fill in the Blanks A first order reaction is 15% complete in 20 It will take to be 60% complete The rate ofreaction is nearly doubled on increasing the temperature by 275 CHEMICAL KINETICS & CATALYSIS Order of reaction for the hydrolysis of ethyl acetate by HCI is For a reaction A ~Products, the rate law is reaction is ~ = k [A]/2 The order of t The order of reaction of decomposition of H20 is 14 If the rate constant, k = ! -x()' the order of reaction is t a a-x If the rate constant has tl-te UnIt sec-\ the order of reaction is The equation k = Ae- EIRT is known as equation In equation k = Ae- EIRT, A is known as The hydrolysis of ethyl acette in acidic medium is order reaction A substance which changes the rate of reaction is known as The substance which retards the reaction rate is known as cataryst The of a catalyst increases when it is finely divided The substance which increases the efficiency of a catalyst is known as 15 In the conversion of urea into ammonium carbonate acts as a catalyst 16 2502 + O2 ~ 2S0 is an example of catalysis 17 CH 3COOCH + H20~ CH 3COOH + C 2H50H is an example of catalysis 10 11 12 13 18 19 20 He! ~ 2NH , Mo acts as In N2 + 3H2 ~ A catalyst poison is essentially a The presence of a catalyst the activation energy of the reaction True or False State whether the following statements are true (T) or false (F)? ,, 10 11 12 13 14 The value of temperature coefficient is nearly 10 All radioactive emanations are of first order The inversion of cane sugar by HCI is of second order The reaction rate is proportonal to the surface area of reactant The half life period of a first order reaction is O.~93 Order of reaction and molecularity are similar Order of reaction can even be or more Most of the reactions are of first and second order hv The reaction H2 + Cl ~ 2HCI is of zero order The rate of zero order reaction depends on the concentration of the reactant A catalyst is a substance which can only increase the reaction rate When one of the products formed in the reaction itself acts as a catalyst, the phenomenon is called auto-catalysis A catalyst is specific in action A catalyst can change the position of equilibrium 276 15 16 17 18 19 20 21 22 PHYSICAL CHEMISTRY-I A catalyst remains unchanged in mass and chemical composition at the end of a reaction A large quantity of catalyst is required to bring about a reaction The substance which increases the activity of a catalyst is called an activator A promoter decreases the peaks and cracks on the catalyst surface Enzyme ptyalin present in h)lman saliva changes starch into glucose The presence of a catalyst increases the activation energy of the reaction In homogeneous catalysis, the intermediate compound is formed at lower activation energy A catalyst cannot be recovered unchanged chemically at the end of the reaction ANSWERS (a) ,2 (b) (b) (c) (b) (a) (b) (c) (a) 10 (d) 11 (c) 12 (d) llWK~~~~~nWm~~~·Wn~nWn~u~ 25 (a) 26 (c) 27 (b) 28 (b) 29 (c) 30 (a) 31 (c) 32 (a) 33 (d) 34 (d) 35 (a) 36 (c) 37 (b) 38 (c) 39 (c) 40 (c) 41 (b) 42 (d) 43 (c) 44 (b) 45 (d) 46 (a) 47 (c) 48 (d) 49 (d) Fill in the Blanks 13 17 112.8 one Frequency factor efficiency autolhomogeneous 10 14 18 W'C two First promoter promoter 11 15 19 (F) one one Catalyst Urease inhibitor 10 14 18 22 (T), (F), (F), (F), 11 (F), 15 (T), 19 en, 12 16 20 112 Arrhenius negative homogeneous decreases True or False 13 17 21 (F), (T), (T), (T), (T), (T), (F); (F), (F), (F) 12 16 20 en, (T), (T), (F), (F), DOD ... system Oi) Triethyl-amine water system 12 6 IPhase Equilibrium I 10 11 12 13 14 15 16 11 4 11 8 12 2 -12 9 13 1 13 1 13 4 13 7 13 8 14 0 14 2 14 3 14 3 14 4 14 4 14 7 15 0 15 4 (x) (b) (iii) Nicotine-water system... 47 71 4786 4800 4 814 4829 4843 4857 48 71 4886 4900 13 4 678 JO 11 13 31 4 914 4928 4942 4955 4969 4983 4997 5 011 5024 5038 34 678 JO 11 12 32 50 51 5065 5079 5092 510 5 511 9 513 2 514 5 515 9 517 2 13 4... = 1; 10 glO 10 = and so on (d) The logarithm of to any base is zero, i.e., loga = 0; logs = 0; 10 glO =0 and so on (e) 10 gJO = 0; 10 gJO 10 = 1; 10 gIO 10 0 = [.: 10 gIO 10 0 = 10 gJO 10 2 = log 10 10