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56 | Chemistry-XII, , UNIT 4, CHEMICAL KINETICS, CONCEPT, Chemical Kinetics : The branch of physical chemistry which deals with the study, of rate of reaction and factors affecting rate., Rate of chemical reaction : The change in concentration of any reactant or, product per unit time is called rate of reaction., Types of Rate of Reaction :, 1., , Average rate of reaction : The rate of reaction measured over the long time, interval is called average rate of reaction., Avg rate x/t = –[R]/t = + [p]/t, , 2., , Instantaneous rate of reaction : The rate of reaction measured at a particular, time is called instantaneous rate of reaction., (Rate)i = (Instantaeous rate) dx/dt = –d[R]/dt=+d[P]/dt, , Factors affecting Rate of Reaction, 1., , Concentration of reactant, , 2., , Surface area, , 3., , Temperature, , 4., , Nature of reactant, , 5., , Presence of catalyst, , 6., , Radiation in photochemical reaction, , Rate constant (k) : It is equal to the rate of reaction when molecular concentration, of reactant is at unity., Rate law : The rate of reaction is directly proportional to the product of, concentration of reactant and each concentration is raised to some power which may or, may not be equal to stereochemistry experimentally., For a reaction,, , aA + bB  cC + dD

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Chemical Kinetics | 2, , Rate law = k[A] [B], p, , q, , where powers p and q are determined experimentally., Molecularity : The total number of reactants taking part in elementary chemical, reaction is called molecularity., Order of reaction : The sum of powers to which the concentration terms are, raised in a rate law expression is called order of reaction., For above case,, , Order = P + Q, , Orders of reaction is determined experimentally., Half-life period : The time during which the concentration of the reactant is, reduced to half of its initial concentration is called half-life period., Activation energy : The minimum extra amount of energy absorbed by reactant, molecules so that their energy becomes equal to the threshold energy is called activation, energy., Activation energy = Threshold energy – Kinetic energy, Temperature coef cient : The ratio of rate constant at two temperatures having, difference of 10ºC is called temperature coef cient., Temperature coef cient = Rate constant at T + 10ºC/Rate constant at TºC, Arhenius Equation :, K = AeEa/RT, where,, , K = Rate constant, A = Arrhenius energy (Frequency factor or pre-exponential factor), Ea = Activation energy, R = Rate constant, T = Temperature, = Fraction of molecules having energy equal to or more than activation, energy, , Log K = Log A –, , Log

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3 | Chemistry-XII, , Enery of activation can be evaluated as :, Log[K2/K1] = Ea (1/T1-1/T2)/2.303RT, Log[K2/K1] = Ea(1/T1-1/T2) / 19.15, 1., , Integrated rate law equation for zero order reaction is given as below :, (a) k =, Where k is rate constant and [R]0 is initial molar concentration., (b) t1/2 =, , 2., , t1/2 is half-life period of zero order reaction., , Integrated rate law equation for rst order reaction :, , , (a) k =, , where k is rate constant, [R]0 is initial molar concentration and [R] is, concentration at time 't'., , nal, , (b) Half-life period (t1/2) for rst order reaction :, t½ =, Pseudo chemical reaction : The chemical reaction which looks like higher order, reaction but in real it follows lower order reaction., CH3COOC2H5 + H2O CH3COOH + C2H5OH, Rate = k[CH3COOC2H5]1, Order = 1, , VERY SHORT ANSWER TYPE QUESTIONS (1 Mark), Q. 1. The gas phase decomposition of acetaldehyde, CH3CHO  CH4 + CO, follows the rate law, Rate = k(PCH3CHO)3/2, unit of P is atm and time is second., What are the units of its rate constant ?, Ans. Atm-½ sec-1, Q. 2. State the order with respect to each reactant and overall reaction., H2O + 3I + 2H+  2H2O + I3Rate = k[H2O2]1[I-]1, Ans. Order of reaction = 1 + 1 = 2

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Chemical Kinetics | 4, , Q. 3. Give one example of pseudo rst order reaction., Ans. Hydrolysis of an ester :, CH3COOC2H5 + H2O  CH3COOH + C2H5OH, Q. 4. The rate law for a reaction is, Rate = K [A] [B]3/2, Can the reaction be an elementary process ? Explain., Ans. No, an elementary process would have a rate law with orders equal to its, molecularities and therefore must be in integral form., Q. 5. For the reaction 3H2 + N2  2NH3, how are the rate of reaction expressions, , , Ans. , ,  , ,  , , , , , , , , inter-related ?, , , , Q. 6. Identify the order of a reaction from the following rate constant :, k = 2.3  105 L mol-1 s-1, Ans. Second order, Q. 7. After ve half-life periods for a rst order reaction, what fraction of reactant, remains ?, Ans., Q. 8. Give the damaging effect of photochemistry., Ans. The colour of fabrics fades away on exposure to sunlight., Q. 9. What is the effect of adding catalyst on the free energy of a reaction ?, Ans. No change in G., Q.10. What value of k is predicted for the rate constant by Arrhenius equation is T,   ? Is this value physically reasonable ?, Ans. From the equation, feasible., , , , , , if T   k  A so that Ea = 0. This is not, , Q.11. Determine the order of reaction :, Step 1., , 2NO + H2  N2 + H2O2, , Slow, , Step 2., , H2O2 + H2  2H2O, , Fast

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5 | Chemistry-XII, , Ans., , Rate = k [NO]2 [H2], Order = 2 + 1, =3, , Q.12. What is the order of reaction whose rate constant has the same units as the, rate of reaction ?, Ans. Zero order, Q.13. Why are reactions of higher order less in number ?, Ans. A reaction takes place due to collide of molecules. The chances for a large number, of molecules or ions to collide simultaneously are less. Hence, the reactions of, higher order are less., Q.14. What will be the effect of temperature on rate constant ?, Ans. Rate constant of a reaction is nearly doubled with rise in temperature by 10º., Q.15. State a condition under which a bimolecular reaction is kinetically rst order, reaction., Ans. A bimolecular reaction becomes rst order reaction when one of the reactants is, in excess., Q.16. Why can’t molecularity of any reaction be equal to zero ?, Ans. Molecularity of a reaction means the number of molecules of the reactants taking, place in an elementary reaction. Since at least one molecule must be present, so, that molecularity will be atleast one., Q.17. Give an example of zero order reaction., Ans., , , , , , or any other example, , Q.18. The rate constant of a reaction is 3  102 min-1. What is its order of reaction ?, (On the basis of units of rate constant), Ans. First order reaction., Q.19. Three-fourth of a reaction is completed in 32 minutes. What is the half life, period of this reaction ?, Ans. 16 minutes., Q.20. What is meant by an elementary reaction ?, Ans. A reaction which takes place in one step is called an elementary reaction. For, example : H2 + I2  2HI., Q.21. Give one example of a reaction where order and molecularity are equal ?, Ans. 2HI  H2 + I2 (Order = Molecularity = 2)

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Chemical Kinetics | 6, , Q.22. For a reaction R  P, the rate becomes 2 times when the concentration of the, reactant A is increased 4 times. What is the order of reaction ?, Ans. r = k(a)n  2r = k(4a)n  2 = 4n  n = 0.5, Q.23. The rate constant of a zero order reaction in A is 0.003 mol L-1 sec-1. How long, will it take for the initial concentration of A to fall from 0.10M to 0.075 M ?, Ans., , , ,     , , , , , , Q.24. In a reaction 2A  Products, the concentration of A decreases from 0.5 mol, L-1 in 10 minutes. Calculate the rate during this interval., Ans. Average rate =, ,  , , , , , , , , , , , ,  , , , , , , , Q.25. In some cases large number of colliding reactant molecules have energy more, than threshold energy even then the reaction is slow. Why ?, Ans. Because resultant molecules do not collide in proper orientation., Q.26. Give an example of a reaction having fractional order., Ans. Decomposition of acetaldehyde (order = 1.5)., , , , , , , Q.27. Decomposition reaction of ammonia on 1t surface has rate constant = 2.5 , 10-1 mol L-1 sec-1. What is order of reaction ?, Ans. Unit of k explain that it is zero order reaction., Q.28. What is order of radioactive decay ?, Ans. First order, Q.29. For a reaction A + B  Product, the rate low is given by r = k[A]½ [B]2. What, is the order of the reaction ?, Ans. Order of reaction = ½ + 2 = 2.5, SHORT ANSWER-I TYPE QUESTIONS (2 Marks), Q. 1. The rate of a particular reaction quadruples when the temperature changes, from 293 K to 313 K. Calculate activation energy., Ans., , K2/K1 = 4, T1 = 293 K, T2 = 313 K, , , , , , , , , , , 

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7 | Chemistry-XII, , Thus, on calculating and substituting values, we get :, Ea = 52.86 KJ mol-1, Q. 2. If the decomposition of nitrogen oxide as, 2N2O5  4NO2 + O2, follows a rst order kinetics., (a) Calculate the rate constant for a 0.05M solution if the instantaneous rate, is 1.5  106 mol/l/s ?, Ans., , Rate, K, , = K[N2O5], =, , =, K, , , , , , , , , = 3.0  105, , (b) What concentration of N2O5 would give a rate of 2.45  105 mol L-1 s-1 ?, Ans., , Rate, , [N2O5], , = 2.45  105 mol L-1 s-1, , =, , , , , , , , = 0.82 M, Q. 3. Write the difference between order and molecularity of reaction., Ans., Order, Molecularity, 1. It is the sum of the powers of concentration It is the number of reacting species, terms in the rate law expression., undergoing simultaneously collision in, a reaction., 2. It is determined experimentally., , 2. It is a theoretical concept., , 3. Order of reaction need not to be a whole num 3. It is whole number only., ber., 4. Order of reaction can be zero., , 4. It can’t be zero or fractional.

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Chemical Kinetics | 8, , Q. 4. The rate constant for a reaction of zero order A is 0.0030 mol L-1 s-1. How long, will it take for the initial conc. of A to fall from 0.10M to 0.075M ?, Ans. For a zero order reaction,, K = 0.0030 mol L-1 s-1, [A]0 = 0.10M, , [A] = 0.075M, ,    , , K =, , , , t=, , , , Q. 5. For the reaction :, C6H12O6 + C6H12O6, (a) Rate of reaction expression., (b) Molecularity, , , , Ans. (a) Rate = , =, ,  , , , ,  , , , , , , (b) Molecularity = 2, Q. 6. Consider the decomposition reaction :, , , , , , , , , This reaction takes place in two steps as given below :, Step 1., , H2O2 + I  H2O + IO (slow), , Step 2., , H2O2 + IO  H2O + I + O2 (fast), , (a) Determine rate law expression., (b) Determine the order of reaction., Ans. (a) Rate = K[H2O2][I-] because second step is rate determining step., (b) Order = 1 + 1 = 2, Q. 7. The decomposition of hydrocarbon follows the equation K = (4.5  1011 s-1), e-28000k/T. Calculate Ea., Ans., , K = (4.5  1011 s-1) e-28000k/T, Comparing the equation with Arrhenius equation,

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9 | Chemistry-XII, , K = AeEa/RT, , , , Ea = 28000  8.314, = 232192 J mol-1, , Q. 8. For a reversible reaction,, , ˆ ˆˆ ˆ†, ‡, ˆˆ, , , , derive an expression for the formation of HI., Ans., , Rate of reaction =, ,  , , = k1[H2] [I2] – 2k2[HI]2, Rate of formation of HI = 2k1[H2] [I2] – 2k2[HI] 2, Q. 9. A reaction is of second order with respect to a reactant. How is the rate of, reaction affected if the conc. of the reactant is reduced to half. What is the, unit of rate constant for such a reaction ?, Ans., , Rate = k[A]2, , , Unit of k =, , = k(mol-1)2, , k = mol-1 L S-1, Q.10. For a rst order reaction time taken for half of the reaction to complete is t1, and ¾ of the reaction to complete is t2. How are t1 and t2 related ?, Ans. t2 = 2t1 because for 3/4th of the reaction to complete time required is equal to two, half lives., Q. 11.

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Chemical Kinetics | 10, , (a) What is the order of the reaction ?, (b) What is the slope of the curve ?, Ans. (a) Zero order reaction., (b) [R] = [R0] – kt,  Slope = – k, Q.12. Derive an expression to calculate time required for completion of zero order, reaction., Ans. For a zero order reaction,, R = [R]0 – kt, For completion of the reaction [R] =0, , , kt = [R]0, , Or, , t=, ,  , , Q.13. For the reaction N2 (g) + 3H2 (g)  2NH3 (g), How is the rate of formation of ammonia related to the rate of disappearance, of H2 ?, Ans. Rate of reaction, , Or, , , , , = , , , , , , , , , , , , , , , , , , , , Q.14. The rate of a gaseous reaction becomes half when volume of the vessel is, doubled. What is the order of reaction ?, Ans. Suppose, order of reaction is n and the reaction is A (g)  Products, ...(i), , Rate = k[A]n, , When volume is doubled, molar conc. becomes half and rate of reaction gets, halved., , , , ,  , , , , , , ...(ii)

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11 | Chemistry-XII, , Dividing equation (i) by equation (ii),, (2)1 = (2)n, Or, , n=1, , Q.15. A reaction which is rst order with respect to A has rate constant 6 min-1. If, we start with [A] = 0.5 mol L-1, when would [A] reach the value of 0.05 ML-1 ?, , , Ans., ,  ,  , , k = 6 min-1, [A]0 = 0.5, [A] = 0.05, t = ?, , , , , , , Q.16. The conversion of the molecules X to Y follows second order kinetics. If the, concentration of X is increased to three times, how will it affect the rate of, formation of Y ?, Ans. 9 times, Q.17. A rst order reaction has a rate constant 1.15  10-3 s-1. How long will 5 gram, of this reactant take to reduce to 3 grams ?, Ans. t = 444 seconds, Q.18. 4NH3 + 5O2  4NO + 6H2O. If rate of formation of NO is 6  104 atm min-1,, calculate the rate of formation of H2O., Ans. 9.0  104 atm min-1, Q.19. A rst order reaction is 75% completed in 60 min. Find the half life of this, reaction., Ans. 30 mins., Q.20. The composition of a hydrocarbon follows the equation K = (4.5  1011 sec-1), e-28000K/T. Calculate the value of Ea., Ans. 232.79 kJ/mol, Q.21. Consider a certain reaction A  Product with K = 2.0  10-2 s-1. Calculate the, concentration of A remaining after 100 s, if the initial concentration of A is, 1.0 mol L-1., Ans. [A] = 0.135 M

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Chemical Kinetics | 12, , Q.22. Explain with an example, what is a pseudo rst order raction ? The graphs (A, and B) given below are plots of rate of reaction Vs concentration of the reactant., Predict the order from the graphs., , Q.23. Differentiate between :, (a) Average rate and instantaneous rate of a chemical reaction., (b) Molecularity and order of reaction., Q.24. Show that in case of rst order reaction, the time required for 99.9% of the reaction, to take place is about ten times than that required for half the reaction., Q.25. For the reaction NO2 + CO  CO2 + NO, the experimentally determined rate, expression below 400 K is rate = k[NO2]2. What mechanism can be proposed for, this reaction ?, Q.26. The half life period of a rst order reaction is 60 min. What % will be left, after 240 mins. ?, Ans. 6.25%, Q.27. Time for half change for a rst order reaction is 25 min. What time will be, required for 99% reaction ?, Ans. 166.16 mins., , SHORT ANSWER TYPE-II QUESTIONS, Q. 1. The rate constant for rst order reaction is 60/s. How much time will it take, to reduce the concentration of the reaction to 1/10 of its initial value ?, Ans., , , , , , , , , , , , , , , , 

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13 | Chemistry-XII, , , = 3.38  10-2 s-1, Q. 2. The rate of most of reaction double when their temperature is raised from, 298 K to 308 K. Calculate the activation energy of such a reaction., , , Ans., , , , , , , , , , , , , Ea = 52.89 KJ/mol, Q. 3. A rst order reaction takes 69.3 min for 50% completion. Set up on equation for determining the time needed for 80% completion., , , Ans., , , , = 10-2 min-1, ,  ,  , , , , , , , , = 160.9 min, Q. 4. The rate constant of a reaction is 1.2  10-3 sec-1 at 40º C. Calculate the, energy of activation of the reaction., Ans., , K1 = 1.2  10-3 sec-1, , T1 = 30 + 273 = 303 K, , K2 = 2.1  10-3 sec-1, , T2 = 40 + 273 = 313 K, , Using,, , , , , , , , , , , , 

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Chemical Kinetics | 14, , , , Ea = 44.13 KJ mol-1, , Q. 5. The activation energy of a reaction is 94.14 KJ/mol and the value of rate, constant at 40º C is 1.8  10-1 sec-1. Calculate the frequency factor A., Ans. Given, Ea = 94.14  103 J mol-1, T = 40 + 273 = 313 K, K = 1.8  10-1 sec-1, By using,, A = antilog (10.9635) = 9.194  1010 sec-1, Q. 6. The rate constant of a reaction at 500 K and 700 K are 0.02 s-1 and, 0.07 s respectively. Calculate the value of Ea and A., Ans. 18.23 KJ mol-1, 1.603, -1, , Q. 7. The rate constant of a reaction at 700 K and 760 K are 0.011 M-1 s-1 and, 0.105 M-1 s-1 respectively. Calculate the value of Arrhenius parameters., Ans. 2.824  1010, , Q. 8. The initial concentration of N2O5 in the rst order reaction N2O5  2NO2, + ½O2 was 1.24  10-2 mol L-1 at 318 K. The concentration of N2O5 after 60, minutes was 0.20  10-2 mol L-1. Calculate the rate constant of the reaction, at 318 K., Ans.

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15 | Chemistry-XII, , Q. 9. The following data were obtained during the rst order thermal decomposition of N2O5 at constant volume :, 2N2O5  2N2O4 + O2, S. No., , Time per second, , Total pressure (atm), , 1, , 0, , 0.5, , 2, , 100, , 0.512, , Calculate rate constant., Ans. 4.98  104 sec-1, Q. 10. A rst order reaction is 20% complete in 20 minutes. Calculate the time, taken for the reaction to go to 80% completion., Ans. 144.3 minutes, Q. 11. For a rst order reaction, calculate the ratio between the time taken to complete ¾ of the reaction and the time taken to complete half of the reaction., Ans. Two, Q. 12. The following results have been obtained during the kinetics studies of the, reaction :, 2A + B  C + D, Experiment, , [A] mol L-1, , [B] mol L-1, , Initial rate of formation, of D mol L-1 min-1, , I, , 0.1, , 0.1, , 6.0  10-3, , II, , 0.3, , 0.2, , 7.2  10-2, , III, , 0.3, , 0.4, , 2.88  10-1, , IV, , 0.4, , 0.1, , 2.40  10-1, , Determine the rate law and the rate constant for the reaction., Ans. Rate = K[A][B], Q. 13. The rate of reaction triples when the temperature changes from 293 K to, 313 K. Calculate the energy of activation of the reaction assuming that it, does not change with temperature., Q. 14. A rst order reaction takes 40 m,ins for 30 decomposition. Calculate t½., Ans. 77.7 mins., Q. 15. The decomposition of A into product has value of K as 4.5  103 sec-1 at 10º, C and energy of activation 60 kJ/mol. At what temperature would K be, 1.5  104 sec-1., Ans. 24º C

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Chemical Kinetics | 16, , Q. 16. The rate of formation of NO is 3.6  10-3 mol L-1 sec-1. Calculate the rate of, disappearance of NH3 and rate of formation of H2O., Ans. 3.6  10-3 Ms-1, 5.4  10-3 Ms-1, Q. 17. (a) Write rate law and order of the following reaction :, AB + C2  AB2C + C (slow), AB2 + C  AB2C (fast), (b) De ne energy of activation of a reaction., (c) What is the relationship between rate constant and activation energy of, a reaction ?, Ans. (a) Rate = K[AB2][C2], Order = 1 + 1 = 2, (c), , , , , , Q. 18. For a chemical reaction R  P, the variation in the concentration (R) vs time (t), plot is given :, , (a) Predict the order of reaction., (b) Write down its rate law., (c) What is the slope of the curve ?, Q. 19. What do you understand by a rst order reaction ? Show that for a rst, order reaction time required to complete a de nite fraction of the reaction, is independent of initial concentration., Q. 20. In a pseudo rst order reaction of hydrolysis of an ester in H2O, the following results were obtained :, t/s, Ester (M/L), , 0, , 30, , 60, , 90, , 0.55, , 0.31, , 0.17, , 0.085, , (a) Calculate the average rate of reaction between the time interval 30 to, 60 sec., (b) Calculate the pseudo, ester., , rst order rate constant for the hydrolysis of, , Ans. (a) Average rate during 30-60 sec. , , , , , , , , , , , , , 

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17 | Chemistry-XII, ,  ,  , , , , (b), , , , , , , Average K = 1.98  10-2 sec-1, Q. 21. Following reaction takes place in one step :, 2NO + O2  2NO2, How will the rate of the reaction of the above reaction change if the volume, of reaction vessel is diminished to 1/3 of its original volume ? Will there be, any change in the order of reaction with reduced volume ?, Ans. 2NO + O2  2NO2, dx/dt = K*[NO]2[O2]1, [Since it is one step.], If the volume of reaction vessel is diminished to 1/3, conc. of both NO and O2, will become 3 times, the rate of reaction increased 27 times in the order of reaction with the reduced volume., Q. 22. The decomposition of NH3 on platinum surface is a zero order reaction., What are the rate of production of N2 and H2 ? [K = 2.5  104], Ans., , 2NH3  N2 + 3H2, , , , ,  , , , , , , , ,  , ,  , , , , = 2.5  104 mol L-1 sec-1, ,  , , , , , , , , , , , , , 

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Chemical Kinetics | 18, , , ,  , , , , , , , , , , = 3.75  1044 mol L-1 sec-1, , , , , , , , , , , = 2.5  104 mol L-1 sec-1, Rate of production of N2 = 2.5  104 mol L-1 sec-1, , LONG ANSWER TYPE QUESTIONS, Q. 1. (a) De ne order of reaction., (b) Rates of reaction double with every 10º rise in temperature. If this, generalization holds for a reaction in the temperature ranges 298 K to, 308 K, what would be the value of activation energy for their reaction ?, R = 8.314 J K-1 mol-1., Ans. (a) Order of Reaction : It is the sum of powers to which the conc. terms are, raised in rate law expression., , , , , , , , (b), Here,, , , , , , , , T1 = 298 K, T2 = 308 K, R = K-1 mol-1, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , = 52898 J mol-1, = 52.898 KJ mol-1, Q. 2. (a) What are pseudo chemical reaction ? Give example., (b) Rate constant K of a reaction varies with temperature ‘T’ according to, the equation :

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19 | Chemistry-XII, , , ,  ,  ,  , , , , where Ea is the activation energy. When a graph is plotted for log K vs 1/T,, a straight line with a slope of  4250 K is obtained. Calculate Ea for the, reaction., Ans. (a), , Slope =, , So,, , =  4250 K, , Ea =  2.303  R  Slope, =  2.303  8.314 J K-1 mol-1  4250, = 81375.3 J mol-1, = 81.375 KJ mol-1, , (b) The chemical reaction which look like higher order reaction but in real they, follow lower order kinetics., For example,, CH3COOC, H + H2O, 2 5, excess, , , ,  CH5COOH + C2H5OH, , Rate = K[CH3COOC2H5], Order = 1, Q. 3. (a) Determine the units of rate constant for rst and zero order reaction., (b) Show that time required for the completion of 99% of the, order, reaction is twice the 90% of completion of the reaction., Ans. (a), , K = (mol)1 – n Ln – 1 S–1, For zero order, n = 0, So,, , K = (mol)1 – 0 L0 – 1 S–1 = S–1 mol L–1, , For rst order, n = 1, K = (mol)1 – n Ln – 1 S–1, So,, , K = (mol)1 – 1 L1 – 1 S–1, = S–1, , (b) For a rst order reaction,, , ,  ,  , , rst

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Chemical Kinetics | 20, , [A]0 = a,, , = 0.01 a, , ...(i), For 90% completion of reaction,, , ...(ii), Dividing equation (i) by equation (ii), we get, t(99%) = 2  t(90%), Q. 4. (a) De ne rate constant of reaction., (b) A rst order reaction takes 40 mins for 30% decomposition. Calculate, t½., Ans. (a) Rate constant : It is the rate of chemical reaction when the concentration of, reactant taken as unity at a given temperature., (b) Let initial conc. = a, Conc. after 40 mins. =, = 0.70 a

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21 | Chemistry-XII, , , , , , = 8.92  10–3 min–1, , , , , , , , , = 77.7 min, , Q. 5. (a) Determine the order of reaction and also determine the units of rate, constant., , (b) The following data were given for thermal decomposition of SO2Cl2 at, a constant volume :, SO2Cl2 (g)  SO2 (g) + Cl2 (g), Exp., , Time/s, , Total p/atm, , 1, , 0, , 0.5, , 2, , 100, , 0.6, , Calculate the rate of the reaction when total pressure is 0.65 atm., Ans. (a) First order reaction, K = mol1 – n Ln – 1 S–1, n=1, K = (mol)1 – 1 L1 – 1 S–1, = S–1, (b), , , , , , , , , , , , 0.4, , , , , , , , 

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Chemical Kinetics | 22, , , , , , , , , , , , , , Now, Rate = PSO Cl, , 2 2, , Pressure of SO2Cl2 when total pressure = 0.65 atm, PSO Cl, , = 2P1 – Pt, , 2 2, , = 2  0.5 – 0.65, = 0.35 atm, Rate = 2.23  10–3  0.55, = 7.8  10–4 atm S–1, Q. 6. (a) The activation energy of a reaction is 100 kJ/mol. In the presence of, catalyst the activation energy is decreased by 75%. What is the effect on, rate constant of the reaction at 20º C ?, (b) A + 2B  3C + 2D, The rate of disappearance of B is 1  10–2 mol L–1 sec–1. What will be, (i) rate of reaction (ii) rate of change in the concentration of A and C ?, Ans. (a) 2.35  1013 times, [Hint :, , , , , , , , , , , , , , , ], , (b) (5  10–3, 5  10–3, 15  10–3) M L–1 sec–1, Q. 7. (a) For the reaction 2A + B ® A2B, the rate = k[A][B]2 with k = 2.0  10–6 mol–2 L2 sec–1. Calculate the initial, rate of reaction when [A] = 0.1 mol L–1, [B] = 0.2 mol L–1. Calculate the rate, of reaction after [A] is reduced to 0.06 mol L–1., (b) (i) The activation energy for the reaction 2HI  H2 + I2 is 209.5 KJ/mol at, 581 K. Calculate the fraction of molecules of reactants having energy, equal to or greater than activation energy., (ii) The activation energy of a reaction is zero. Will the rate constant of the, reaction depend upon temperature ? Give reason., Ans., , , if Ea = 0, then K = A. Frequency factor (A) does not depend upon, , temperature, therefore, rate constant and rate does not depend on temperature., , Q. 8. The concentration of R in the reaction R  P was measured as a function of time, and the following data is obtained :

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23 | Chemistry-XII, , [R] molar, t (in min), , 1.0, 0.0, , 0.75, 0.05, , 0.40, 0.12, , 0.10, 0.18, , Calculate the order of the reaction., [Hint : Determine the rate of reaction at different intervals of time. It comes out, to be constant. Hence, it is a zero order reaction.], , VALUE BASED QUESTIONS (4 Marks), Q. 1. Food and dairy products get spoiled more quickly in summer. Therefore, use of, refrigerator has became very common in almost every house. Sita, a class XII, Chemistry student, suggested her mother to store milk and other dairy products, in refrigerator and not in open on kitchen slab., (a) Why Sita suggested her mother to store milk and dairy products in the, refrigerator ?, (b) Mention the relationship to express how rate of reaction is related with, temperature., (c) What values are learnt by Sita’s advice ?, (d) Name the food preservative used to prevent spoilage of food., Q. 2. Ramesh tried his best to carry out the reaction between the pure hydrogen, with pure oxygen but he failed. Mohan, a friend of Ramesh, suggested that the, reaction must be carried out in the presence of Pt catalyst. As he placed platinum, in the reaction mixture, the reaction took place explosively., (a) Mention the role of catalyst in the above chemical reaction., (b) What values are associated with the suggestion of Mohan ?, De ne (c) activity and (d) selectivity of a catalyst., Q. 3. Sudha’s mother received a phone call on Monday morning from a close, relative stating that three of them would be coming over for lunch. Sudha’s, mother noticed that she did not have enough curd to serve the guests. Sudha, a, class XII chemistry student, suggested to her mother to take warm milk and keep, it under direct sunlight and curdle it., (a) Why do you think Sudha suggested the above method ?, (b) Will it be helpful if her mother followed Sudha’s suggestion ?, (c) What values are associated with Sudha’s suggestion ?, (d) Name the bacteria responsible for curdling of milk.