Mechanism multiple choice questions

Question 1) For a reaction 2A + B 2C, with the rate equation: Rate = k[A][B]2

a) The order with respect to A is 1 and the order overall is 1. b) The order with respect to A is 1 and the order overall is 3. c) The order with respect to A is 2 and the order overall is 3. d) The order with respect to B is 2 and the order overall is 2. e) The order with respect to B is 1 and the order overall is 3.

Question 2) In a reaction mechanism, the rate determining step is the:

a) Fastest and has the lowest activation energy.b) Fastest and has the highest activation energy.c) Slowest and has the lowest activation energy.d) Slowest and has the highest activation energy.

Question 3) What are the units of k when; r = k[A][C]?

a) s-1 b) s c) dm3 mol-1 s-1 d) dm2 mol-2 s-1 e) dm3 s2 mol-2

Question 4) Consider the following reaction mechanism:Step1: ICl + H2 → HI + HCl slowStep 2: ICl + HI → HCl + I2 fastThe species HCl is a:

a) productb) catalystc) reactantd) reaction intermediate

Question 5) Suppose the reaction: A + 2B AB2 occurs by the following mechanism:

Step 1 A + B AB slowStep 2 AB + B AB2 fastOverall A + 2B AB2

The rate equation must be r =

a) k[A] b) k[B] c) k[A][B] d) k[B]2 e) k[A][B]2

Question 6) A possible mechanism for the reaction, 2A + B C + D, is: (1) A + A A2 fast, equilibrium(2) A2 + A A3 slow(3) A3 + B A + C + D fast

According to the mechanism, the rate equation will be:

a) Rate = k[A]2 b) Rate = k[A][B] c) Rate = k[A]2[B] d) Rate = k[A]3

e) Rate = k[A] [A2]

Question 7) At 300 K, the following reaction is found to obey the rate law: Rate = k[NOCl]2: 2NOCl 2NO + Cl2

Consider the three postulated mechanisms given below. Then choose the response that lists all those that are possibly correct and no others.

Mechanism 1 NOCl NO + Cl slowCl + NOCl NOCl2 fastNOCl2 + NO 2NO + Cl2 fastOverall: 2NOCl 2NO + Cl2

Mechanism 2 2NOCl NOCl2 + NO slowNOCl2 NO + Cl2 fastOverall: 2NOCl 2NO + Cl2

Mechanism 3 NOCl NO + Cl fast, equilibriumNOCl + Cl NO + Cl2 slowOverall: 2NOCl 2NO + Cl2

a) 2, 3 b) 3 c) 1 d) 2 e) 1, 2

Question 8) A correct reaction mechanism for a given reaction usually is:

a) The same as its balanced chemical equation. b) Obvious if its heat of reaction is known. c) Obvious if its reaction order is known. d) Sometimes difficult to prove. e) Obvious if its activation energy is known.

Question 9) For the reaction, 2H2S(g) + O2(g) 2S(s) + 2H2O(l), which one of the following statements is absolutely true?

a) The reaction is first order with respect to H2S and second order with respect to O2. b) The reaction is fourth order overall. c) The rate law is: rate = k[H2S]2[O2]. d) The rate law is: rate = k[H2S][O2]. e) The rate law cannot be determined from the information given.

Question 10) Consider the following reaction mechanism:Step 1: V3+ + Cu2+ V4+ + Cu+

Step 2: Cu+ + Fe3+ Cu2+ + Fe2+ slowThe reaction intermediate is:

a) Cu+

b) Cu2+

c) V3+

d) Fe3+

Question 11) Increasing the concentration of which of the following substances would cause the greatest increase in the reaction rate?

Step 1 2NO N2O2 FastStep 2 N2O2 + H2 H2O +N2O SlowStep 3 N2O + H2 N2 +N2O Fast

a) H2

b) NOc) N2Od) H2O

Question 12) A proposed mechanism for a reaction is…

Step 1 H3O+ + I- HI + H2O FastStep 2 H2O2 + HI H2O + HOI SlowStep 3 HOI + H3O+ + I- 2H2O + I2 FastStep 4 I2 + I- I3

- FastThe rate equation could be:

a) r = k [H2O2] [HOI]b) r = k [H3O+] [H2O2]c) r = k [H2O2] 2 [HI]2

d) r = k [H2O2] [HI]

Question 13) The rate law for the reaction: 2NO2 + O3 N2O5 + O2 is rate = k[NO2][O3].

Which of the following mechanisms is consistent with this rate equation? a) 2 NO2 → N2O4 fast

N2O4 + O3 → N2O5 + O2 slow b) NO2 + O3 → NO5 fast

2 NO5 → N2O5 + 5/2 O2 slow c) NO2 + O3→ NO3 + O2 slow

NO3 + NO2 → N2O5 fast d) 2 NO2→ N2O2 + O2 slow

N2O2 + O3 → N2O5 fast

Question 14) The reaction H2O2 (aq) + 3I- (aq) + 2H+ (aq) 2H2O (l) + I3

- (aq) has an

observed rate law rate = k [H2O2] [I-] [H+]

A mechanism is proposed for the overall reaction. Which elementary reaction below could be the rate-determining step of the proposed mechanism?

a) H2O2 (aq) + 3 I- (aq) + 2 H+ (aq) → 2 H2O (l) + I3

- (aq)

b) H2O2 (aq) + I- (aq) + 2 H+ (aq) → H2O (l) + OI- (aq)

c) H2O2 (aq) + I- (aq) + H+ (aq) → H2O (l) + HOI (aq)

d) none of these elementary steps can be the rate-determining step