1. Opp. Khuda Baksh Library, Ashok Rajpath, Patna House no. 5A/65, Opp. Mahual Kothi, Alpana Market, Patna

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1 1. Which of the following expressions does NOT represent a proper expression for the rate of this reaction? 2A + 3B F + 2G a) (- [A)/( t) b) (- [B)/(3 t) c) ( [F)/( t) d) ( [G)/(2 t) e) (- [A)/(2 t) 2. Consider a chemical reaction involving compounds A and B, which is found to be first order in A and second order in B. At what rate will the reaction occur in experiment 2? Experiment Rate (M s -1 ) Initial [A Initial [B M 0.20 M 2? 2.0 M 0.60 M a) 1.8 M s -1 b) 0.20 M s -1 c) 1.2 M s -1 d) 0.36 M s -1 e) 0.60 M s A first-order reaction has a rate constant of s -1. The time required for 85% reaction is: a) 23.5 s b) 54.2 s c) 632 s d) 316 s e) 275 s 4. An elementary process has an activation energy of 40 kj/mol. If the enthalpy change for the reaction is 30 kj/mol, what is the activation energy for the reverse reaction? a) 50 kj/mol b) 40 kj/mol c) -40 kj/mol d) 30 kj/mol e) 10 kj/mol 5. If the rate of a reaction increases by a factor of 64 when the concentration of reactant increases by a factor of 4, the order of the reaction with respect to this reactant is: a) 3 b) 16 c) 4 d) 1 e) 2 6. NO reacts with chlorine in a gas phase reaction to form nitrosyl chloride, NOCl. From the following experimental data, determine the form of the equation that describes the relationship of reaction rate to initial concentrations of reactants. 2 NO + Cl 2 2 NOCl Run Initial [NO Initial [Cl 2 Initial Rate of Formation of NOCl M 1.00 M 1.14 M/hr M 1.00 M 9.12 M/hr M 0.50 M 4.56 M/hr a) rate = k[no 3 [Cl 2 b) rate = k[no[cl 2 c) rate = k[no d) rate = k e) rate = k [Cl 2 2 Page No.: 1

2 7. Consider the mechanism: O 3!!!" #!! O 2 + O; fast O + O 3 2 O 2 ; slow An intermediate in this reaction is: a) O 3 b) There is no intermediate in this reaction c) O d) O 2 and O e) O 2 8. The units of the rate constant for a second order reaction could be. a) M s -1 b) M 2 s -1 c) s -1 d) M -1 s -1 e) M 9. When a catalyst is used in a reaction, a) the forward reaction is increased while the reverse reaction is retarded. b) it does not affect the final amounts of reactants and products. c) the enthalpy change for the reaction becomes more exothermic. d) the activation energy of the reverse reaction is increased. e) the activation energy for the forward reaction is not changed Given the following data for the NH 4 + NO 2 N 2 + 2H 2 O reaction: Trial [NH 4+ - Rate M M M/s The rate law for the reaction is: a) rate = k[nh 4+ - b) rate = k[nh c) rate = k[nh d) rate = k[nh e) None of the above 11. The reaction 2 NO 2 2NO + O 2 is postulated to occur via the mechanism below: NO 2 + NO 2 NO + NO 3 ; k 1, slow NO 3 NO + O 2 ; k 2, fast The rate law for this mechanism is: a) rate = k 1 k 2 [NO 3 2 b) rate = k 2 [NO 3 c) rate = k 1 2 d) rate = k 1 k 2 2 [NO 3 e) rate = k Reaction rates increase with increasing temperature because. a) the activation energy is decreased. b) the energy of the transition state is lowered. c) the activation energy increases. d) larger molecules collide more frequently. e) a greater fraction of molecules possess the activation energy when they collide. Page No.: 2

3 13. Consider the following reaction: 2 N 2 O 2 NO + O 2 ; rate = k[n 2 O If the half-life for the reaction is s, the rate constant is: a) 1.1 s -1 b) 0.69 s -1 c) 1.3 s -1 d) 0.32 s -1 e) 0.76 s Given: N H 2 2 NH 3 At equilibrium at a certain temperature, the concentration of NH 3, H 2 and N 2 are M, 1.53 M and M, respectively. Calculate the value of Kc for this reaction. a) 1.26 b) 1.96 c) 3.02 d) e) A large equilibrium constant a) indicates that a reaction has a small rate constant. b) indicates that the reaction favors the formation of reactants. c) indicates that a reaction has a large rate constant. d) indicates that the reaction favors the formation of products. e) results from the addition of a catalyst to a reaction mixture. 16. The relationship between the rate constant and temperature is expressed by the: a) Arrhenius equation b) rate law c) integrated rate equation d) reaction mechanism 17. Identify the INCORRECT statement below: a) The rate of a typical reaction doubles with a 10 C rise in temperature. b) The overall rate of reaction is determined by the rate of the fastest elementary step. c) The reaction mechanism is a step-by-step pathway by which reaction occurs. d) The reaction mechanism is typically a series of elementary reaction steps. e) Reaction orders for a single elementary step are equal to the balancing coefficients for that step. 18. Identify the INCORRECT statement below regarding chemical equilibrium: a) All chemical reactions are, in principle, reversible. b) Equilibrium is achieved when the forward reaction rate equals the reverse reaction rate. c) Equilibrium is achieved when the concentration of species become constant. d) Equilibrium is achieved when the reaction quotient Q equals the equilibrium constant. e) Equilibrium is achieved when the reactant and product concentrations become equal. 19. Write the appropriate equilibrium constant expression K c for the following reaction: 2 CO + O 2 2 CO 2 Page No.: 3

4 a) Kc = k{co 2 [O 2 b) Kc = [O 2 2 c) Kc = d) Kc = [CO[O 2 2 [O Suppose we rewrote the balanced reaction in Problem 19 as: CO + 1/2O 2 Kc CO 2 What would be the equilibrium constant for this reaction? a) same, K c = K c b) K c = sqrt( K c ) 2 c) K c = K c /2 d) K c = K c e) K c = 1/ K c 21. When K c >> 1 for a chemical reaction: a) the equilibrium would be achieved rapidly. b) the equilibrium would be achieved slowly. c) reactants would be much more stable than products. d) product concentrations would be much greater than reactant concentrations at equilibrium. e) reactant concentrations would be much greater than product concentrations at equilibrium. 22. In the rearrangement reaction: cyclopropane propene the equilibrium constant at a certain temperature is K c = 3.0. A reaction vessel initial having a cyclopropane concentration [cyclopropane 0 = 2.0 M and no propene is allowed to come to equilibrium. What will be the concentration of propene at equilibrium? a) 0.0 M b) 0.66 M c) 1.5 M d) 2.0 M For Problems A proposed mechanism for the decomposition of ozone is: (1) O 2 + O (fast, equilibrium) O 3 Ar Ar (2) O + O 3 2O 2 (slow) 23. Which step is rate-determining? a) step (1) b) step (2) Page No.: 4

5 24. Which species is (are) an unstable intermediate? a) O 2 and O b) O 2 c) O d) Ar e) Ar and O 25. Which species is a catalyst? a) O 2 b) O 3 c) Ar d) Ar and O Which is the best overall rate law consistent with this mechanism? a) k[o 3 [O b) k[o 3 2 c) k[o 3 d) k[o 3 2 /[O The properly written overall balanced equation is: a) 2 O 3 3 O 2 b) O 3 2 O 2 c) 2 O 3 + O 3 O 2 + O d) 3 O 2 2 O A reaction with a G o = -30 kj/mol: a) has a K = 0 b) has a positive K but K < 1 c) has a negative K d) has a K > 1 e) has a K = The gas phase reaction A + B C has a reaction rate which is experimentally observed to follow the relationship Rate = k[a 2 [B. If the concentration of A is tripled and the concentration of B is doubled, the reaction rate would be increased by a factor of. a) 9 b) 6 c) 18 d) 12 e) The value of the equilibrium constant for the reaction: 2 HBr H 2 + Br 2 is K c = 1.26 x at 500 K. This implies that: a) the product concentrations will be large relative to the reactants at equilibrium. b) the reaction has a large negative G. c) the rate of this reaction is very slow. d) the reactants are much more thermodynamically stable than the products. Answers: 1. a 2. a 3. c 4. e 5. a 6. a 7. c 8. d 9. b 10. b 11. c 12. e 13. e 14. d 15. d 16. a 17. b 18. e 19. d 20. b 21. d 22. c 23. b 24. c 25. c 26. d 27. a 28. d 29. e 30. d Page No.: 5

Ch 13 Rates of Reaction (Chemical Kinetics)

Ch 13 Rates of Reaction (Chemical Kinetics) Reaction Rates and Kinetics - The reaction rate is how fast reactants are converted to products. - Chemical kinetics is the study of reaction rates. Kinetics