MC – Kinetics
2002
27. A possible mechanism for the overall reaction represented above is the following
(1) NO(g) + NO(g) à N2O2(g) slow
(2) N2O2(g) + O2(g) à 2 NO2(g) fast
Which of the following rate expressions agrees best with this possible mechanism?
(A) Rate = k [NO]2
(B) Rate = k [NO] / [O2]
(C) Rate = k [NO]2 / [O2]
(D) Rate = k [NO]2 [O2]
(E) Rate = k [N2O2] [O2]
47. Which of the following is a correct statement about reaction order?
(A) Reaction order can be determined only from the coefficients of the balanced equation for the reaction.
(B) Reaction order can be determined only by experiment.
(C) Reaction order increases with increasing temperature.
(D) A second-order reaction must involve at least two different compounds as reactants.
Time (days) / 0 / 1 / 2 / 3 / 4 / 5 / 6 / 7 / … / 10 / … / 20% Reactant remaining / 100 / 79 / 63 / 50 / 40 / 31 / 25 / 20 / 10 / 1
55. A reaction was observed for 20 days and the percentage of the reactant remaining after each day was recorded in the table above. Which of the following best describes the order and the half-life of the reaction? (Hint: Graph)
Reaction Order Half-life (days)
(A) First 3
(B) First 10
(C) Second 3
(D) Second 6
(E) Second 10
Rate = k [M] [N]2
57. The rate of a certain chemical reaction between substances M and N obeys the rate law above. The reaction is first studied with [M] and [N] each 1.0 × 10-3 molar. If a new experiment is conducted with [M] and [N] each 2.0 × 10-3 molar, the reaction rate will increase by a factor of
(A) 2
(B) 4
(C) 6
(D) 8
(E) 16
1999
Use the below choices to answer #4
(A) Activation energy
(B) Free energy
(C) Ionization energy
(D) Kinetic energy
(E) Lattice energy
4. The energy required to form the transition state in a chemical reaction
Experiment / Initial [NO](mol L¯1 / Initial [O2]
(mol L¯1 / Initial Rate of
Formation of NO2
(mol L¯1 s¯1)
1 / 0.10 / 0.10 / 2.5 x 10¯4
2 / 0.20 / 0.10 / 5.0 x 10¯4
3 / 0.20 / 0.40 / 8.0 x 10¯3
36. The initial-rate data in the table above were obtained for the reaction represented below. What is the experimental rate la for the reaction?
(A) rate = k[NO] [O2]
(B) rate = k[NO] [O2]2
(C) rate = k[NO]2 [O2]
(D) rate = k[NO]2 [O2]2
(E) rate = k[NO] / [O2]
48. If 87.5 percent of a sample of pure 131I decays in 24 days, what is the half-life of 131I? (Decay is a 1st order)
(A) 6 days
(B) 8 days
(C) 12 days
(D) 14 days
(E) 21 days
1994
17. Relatively slow rates of chemical reaction are associated with which of the following?
(A) The presence of a catalyst
(B) High temperature
(C) High concentration of reactants
(D) Strong bonds in reactant molecules
(E) Low activation energy
23.
Step 1: Ce4+ + Mn2+ ---> Ce3+ + Mn3+
Step 2: Ce4+ + Mn3+ ---> Ce3+ + Mn4+
Step 3: Mn4+ + Tl+ ---> Tl3+ + Mn2+
The proposed steps for a catalyzed reaction between Ce4+ and Tl+ are represented above. The products of the overall catalyzed reaction are
(A) Ce4+ and Tl+
(B) Ce3+ and Tl3+
(C) Ce3+ and Mn3+
(D) Ce3+ and Mn4+
(E) Tl3+ and Mn2+
Circle any catalysts in the steps above and mark out any intermediates
30. The energy diagram for the reaction X + Y ---> Z is shown above. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences?
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I, II, and III
49. The isomerization of cyclopropane to propylene is a first-order process with a half-life of 19 minutes at 500 °C. The time it takes for the partial pressure of cyclopropane to decrease from 1.0 atmosphere to 0.125 atmosphere at 500 °C is closest to
(A) 38 minutes
(B) 57 minutes
(C) 76 minutes
(D) 152 minutes
(E) 190 minutes
2008
Experiment / [X]0 / [Y]0 / Initial Rate of Formation of Z1 / 0.40 / 0.10 / R
2 / 0.20 / 0.20 / ?
26. The table above shows the results from a rate study of the reaction X + Y à Z. If the reaction was first order with respect to X and second order with respect to Y, the intial rate of formation of Z in experiment 2 would be
A. R/4
B R/2
C R
D 2R
E 4R
32. Gasesous cyclobutane undergoes a 1st order reaction to form gaseous butadiene. At a particular temp, the partial pressure of cyclobutene is a reaction vessel drops to one-eight its original value in 124 seconds. What is the half-life for this reaction?
A) 15.5sec B. 31 Sec C. 41.3sec D. 62 sec E. 124sec
66. Factors that affect the rate of a chemical reaction include which of the following?
I. Frequency of collisions of reactant particles
II. Kinetic Energy of collisions of reactant particles
III. Orientation of reactant particles during collisions
A. II only B. I and II only C. I and III only D. II and III only E. All 3
Free Response
1989 D: C2H4(g) + H2(g) ↔ C2H6(g) DH° = –137 kJ
Account for the following observations regarding the exothermic reaction represented by the equation above.
(a) An increase in the pressure of the reactants causes an increase in the reaction rate.
(b) The presence of metallic nickel causes an increase in reaction rate.
(c) The presence of powdered nickel causes a larger increase in reaction rate than does the presence of a single piece of nickel of the same mass.
1990 D: Consider the following general equation for a chemical reaction.
A(g) + B(g) ®C(g) + D(g) DH° reaction = -10 kJ
(a) Describe the two factors that determine whether a collision between molecules of A and B results in a reaction.
(b) How would a decrease in temperature affect the rate of the reaction shown above? Explain your answer.
(c) Write the rate law expression that would result if the reaction proceeded by the mechanism shown below.
A + B ®[AB] (fast)
[AB] + B ®C + D (slow)
(d) Explain why a catalyst increases the rate of a reaction but does not change the value of the equilibrium constant for that reaction.
1991 B: 2 ClO2(g) + F2(g) ®2 ClO2F(g)
The following results were obtained when the reaction represented above was studied at 25°C.
Experiment / Initial [ClO2], (mol.L–1) / Initial [F2], (mol.L–1) / Initial Rate of Increase of [ClO2F],(mol.L–1.sec–1)
1 / 0.010 / 0.10 / 2.4x10–3
2 / 0.010 / 0.40 / 9.6x10–3
3 / 0.020 / 0.20 / 9.6x10–3
(a) Write the rate law expression for the reaction above.
(b) Calculate the numerical value of the rate constant and specify the units.
(c) In experiment 2, what is the initial rate of decrease of [F2]?
(d) Which of the following reaction mechanisms is consistent with the rate law developed in (a). Justify your choice.
I. ClO2 + F2 ®ClO2F2 (fast)
ClO2F2 ®ClO2F + F (slow)
ClO2 + F ®ClO2F (fast)
II. F2 ®2 F (slow)
2 (ClO2 + F ®ClO2F) (fast)