Both molecule A and B are reactants. 1. Looking at this graph, which of these statements is accurate? Both molecule A and B are reactants. A) The rate of formation of Molecule A is always higher than the formation of Molecule B. B) The rate of the reaction based on Molecule A is positive. C) The rate of the reaction based on Molecule A is positive. D)The rate of formation of Molecule B is higher than the rate of consumption of Molecule A at 40 seconds into the reaction. Ans : C

Consider the reaction 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) Suppose that at a particular moment during the reaction molecular oxygen is reacting at a rate of 12.5 M/s. At what rate is ammonia reacting? A. 12.5 M/s C. 3.13 M/s 2.50M/s D. 10.0 M/s Ans : D

3. Which of the following statements is false? The rate law expresses the relationship of the rate of a reaction to the rate constant. The rate law expresses the relationship of the rate of a reaction to the concentrations of the reactants raised to some powers. The overall reaction order is the sum of the powers to which all the reactant concentrations appearing in the rate law are raised. Rate laws are never determined experimentally but result only from theoretical calculations involving the activation energy and the order constant. ANS : C

What is the order of this reaction with respect to H2? 4. H2 + 2 ICl → 2 HCl + I2 What is the order of this reaction with respect to H2? A. Zero order C. 2nd order 1st order D. 3rd order ANS: B [H2] (M) [ICl] (M) Rate (M/s) 1.50 3.20 ´ 10–1 3.00 1.28 6.40 ´ 10–1

Consider the first-order reaction A → B shown below. How many A (grey) and B (black) molecules are present at t =15 s? t = 0 s t = 5 s Ans C A: 8, B: 8 C. C: 2, B: 14 C: 2, B: 2 D. D: 1, B: 15

6. Which of the following is true concerning the relationship between reactant concentration and reaction half-life?   A. For 1st order reactions, the ½ life is independent of the initial reactant concentration. B. For 1st order reactions, the rate constant, k, is determined by the initial reactant concentration. C. For second-order reactions the half-life is independent of the initial reactant concentration. D. For second-order reactions, the half-life remains constant throughout the course of the reaction concentration. Ans A

7. 2N2O5(g) → 4NO2(g) + O2(g) The rate of decomposition of 2N2O5(g) is 2.5 x 10-6 mol/s, so the rate of formation of NO2 is   A. 1.0 x 10-5 mol/s B. 1.3 x 10-6 mol/s C. 2.5 x 10-6 mol/s 5.0 x 10-6 mol/s Answer : D

8. The mechanism for the conversion of ozone to molecular oxygen, 2O3 → 3O2 is as follows: O3 → O + O2 (slow) O + O3 → 2O2 (fast) Which statement is false? O is a catalyst in the mechanism. For the overall reaction, rate = k[O3]. The first step is unimolecular. overall reaction is 1st order. Answer : A

At equilibrium the concentration of the products is 3.21 x 10–4 M 9. An automotive catalytic converter contains solid platinum, palladium, and rhodium compounds and converts NO to N2 and O2. This conversion is an example of which of the following: A. Enzyme catalysis C. Heterogeneous catalysis Homogeneous catalysis D. Sub-program catalysis ANS: C 10. If Kc is 3.21 ´ 10–4, what can you assume is true about the reaction?   At equilibrium the concentration of the products is 3.21 x 10–4 M The reaction favors the products The reaction is slow to reach equilibrium. At equilibrium the concentration of the reactants is larger than the products. ANS: D

11. Consider the following reaction at some high temperature, T.   Br2(g) ↔2Br(g)  When 4.2 moles of Br2 are placed in a 6.0 L vessel, 1.20% of the Br2 dissociates. Calculate Kc at temperature, T. A. 2.6 x 10–2 C. 4.1 x 10–4 3.5 D. 1.9 x 10 -8 ANS : C 12. K1 is the equilibrium constant for the reaction. H3PO4 ↔ H2PO2- + H+ ; K2 is the equilibrium constant for the reaction. H3PO4 ↔ H2PO2- + H+ ; K3 is the equilibrium constant for the reaction. H3PO4 ↔ H2PO2- + H+ ;   What is the value of the equilibrium constant K in terms of K1, K2, and K3 for the reaction, 3 H3PO4 ↔ 3 H2PO2- + 9H+ A. K = 3(K1 + K2 +K3) C. K = (K1 K2 K3)3 K= K1 /(K2 K3) D. K = (K1 K2)/K3 ANS : C

13. Given these two elementary steps and their Kc values, along with the Kc of the overall reaction, which of these statements are true about this system?   (reaction 1) H2S qe HS– + H+ K1 = 9.02 x 10–8 (reaction 2) HS– qe S2– + H+ K2 = 1.10 x 10–19 (total reaction) H2S qe S2– + 2H+ Kfinal = 9.92 x10–27  A. The rate of the forward reaction of reaction 1 is higher than the rate of reverse reaction. B. The rate of the reverse reaction is higher than the rate of the forward reaction in reaction 2. C. The rate of the overall reaction is equal to the equilibrium constant of reaction 1. D. The rate of the overall reaction is equal the multiple of Kc of reaction 1 and 2. Answer ALL are correct

14. For the reaction of A(g) + B(g) ↔ 2C(g) Kc = 1.0 ´10–3 at 500 K.   At this temperature, an equal number of moles of each substance is placed into a 5.0 L container. Which statement is true? To reach equilibrium, the reaction will shift to produce more products To reach equilibrium, the reaction will shift to produce more reactants. The system is at equilibrium. The mole amounts must be given to predict the direction of the reaction. Ans: B 15. The equilibrium constant for the reaction Br2(g) qe 2Br(g) is Kc = 2.64 ´ 10–4 at 1400K. What will the concentration of bromine atoms be if 0.250 mol Br2 comes to equilibrium in a 0.500-L reaction vessel at this temperature? A. 1.15 x 10–2 M C. 8.10 x 10–3M 1.32 x 10–2 M D. 1.62 x 10–2 M Answer A

15. What can you determine about this reaction from this graph? 3H2 + N2 ↔ 2NH3 The reaction reached equilibrium but then was unable to return to equilibrium after an input of NH3. The forward reaction rate increased to consume the added NH3. The reaction never reached equilibrium. The reaction returned to equilibrium by increasing the rate of the reverse reaction. ANS D

16. Consider the following reaction mechanism: step 1: M + X → MX step 2: MX + A → D + X The chemical species MX is a(n) A. catalyst B. inhibitor C. final product reaction intermediate Ans D 17. Which of the following are necessary for successful collisions to occur?   I. Favourable geometry II. Sufficient energy III. Large ΔH A. I only B. I and II only C. II and III only I, II, and III Ans : B