Name: ______KEY______________________
Class time: __________________
Exam 1: Kinetics (Ch. 12) and Equilibrium (Ch. 13)
Show all work and clearly mark all answers for full and partial credit.
_B__ 1. (3 pts) What effect does temperature have on the rate of a reaction?
A. the lower the temperature, the lower the kinetic energy which results in more effective
collisions therefore increasing the rate of a reaction
B. the higher the temperature, the greater the kinetic energy which results in more effective
collisions therefore increasing the rate of a reaction
C. the higher the temperature, the greater the kinetic energy which results in more effective
collisions therefore decreasing the rate of a reaction
2. (11 pts) Given the balanced equation 6CH2 O + 4 NH3  (CH2 )6 N4 + 6 H2 O,
a. (4 pts) Write the rate expression for this reaction.
∆[𝐶𝐶𝐶𝐶2 𝑂𝑂]
∆[𝑁𝑁𝑁𝑁3 ]
∆[(𝐶𝐶𝐶𝐶2 )6 𝑁𝑁4 ]
∆[𝐻𝐻2 𝑂𝑂]
−
= −
= +
= +
6∆𝑡𝑡
4∆𝑡𝑡
∆𝑡𝑡
6∆𝑡𝑡
b. (4 pts) If the rate of NH3 is 2.04 x 10-4 M/s, what is the rate of H2 O?
∆[𝐻𝐻2 𝑂𝑂]
∆𝑡𝑡
6 𝑚𝑚𝑚𝑚𝑚𝑚 𝐻𝐻2𝑂𝑂
= 2.04𝑥𝑥10−4 ∗ (4 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁𝑁𝑁3 ) = 3.06 x 10-4 M/s
c. (3 pts) What is the rate of reaction?
rate of reaction=+
∆[H 2O]
6∆t
=
3.06 x 10-4 M/s
6
= 5.10x𝟏𝟏𝟏𝟏−𝟓𝟓 M/s
3. (11 pts) The following data were measured for the reaction: SO2 (g) + 2Cl2 (g) → SOCl2 (g) + Cl2 O(g)
Experiment
1
2
3
[SO2 ](M)
0.10
0.20
0.20
[Cl2 ](M)
0.10
0.10
0.20
Initial Rate(M/s)
0.25
0.50
2.00
a. (2 pts) What is the order of SO2 ? (Show work or justify your answer) __1st order____
Conc. x 2; rate x 2
b. (2 pts) What is the order of Cl2 ? (Show work or justify your answer) __2nd order____
Conc. x 2; rate x 4
c. (2 pts) What is the rate law for this reaction? Rate = __k[SO2 ][Cl2 ]2 ____________
d. (1 pt) What is the overall order of this reaction? __1+2 = 3_______
e. (4 pts) What is the rate constant (with units)? Show your work! __k = 250 M-2 ·s-1 ______
Experiment 1: 0.25 M/s = k(0.10 M)(0.10 M)2 ; k = 0.25 M/s / (0.0010 M3 )
__D__ 4. (3 pts) Which function of concentration plotted versus time will yield a linear plot for a first
order reactant, A?
a. [A] vs. time
CHM 152, Fall 2016
b. 1/[A] vs time
c. [A]2 vs time
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d. ln [A] vs time
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Name: ______KEY______________________
Class time: __________________
5. Reactant A undergoes a first order reaction with a half-life of 21 minutes at 25°C. The initial
concentration of A is 1.6 M.
a) (5 pts) What will be the concentration of A after 55 min?
k = 0.693 / t1/2 = 0.693 / 21 min = 0.033 min-1
ln [A]t = -kt + ln [A]o = -(0.033 min-1 )(55 min) + ln (1.6) = -1.344996; [A]t = 0.26 M
b) (3 pts) How long will it take the reactant to reach 0.15 M?
ln ([A]t / [A]o ) = -kt;
ln (0.15 M / 1.6 M) / -0.033 min-1; t = 72 minutes
6. (5 pts) Draw a reaction profile in the grid below that shows an endothermic reaction with an
activation energy of 40 kJ/mol. Also label the transition state on the graph.
* Transition State
Potential Energy
60 kJ
50 kJ
40 kJ
30 kJ
20 kJ
Reaction Progress (reactants  products)
7. (12 pts) The following 2-step mechanism was determined for a given reaction. Answer the questions
about each step and the overall equation and rate.
rate law: ___rate = k[H2 ][NO]2 _____
Step 1 (slow): H2 + 2NO  N2 O + H2 O
Step 2 (fast): N2 O + H2  N2 + H2 O
rate law: __rate = k[N2 O][H2 ]____
Overall equation: _2H2 + 2NO  N2 + 2H2 O_____
Is there an intermediate?
Yes
No
If yes, what is it? ___N2 O_______
Is there a catalyst?
Yes
No
Overall rate law: _ Rate = k[H2 ][NO]2 _______
If yes, what is it? ___N/A________
_C_ 8. (3 pts) Which one of the following statements is true regarding chemical equilibrium?
a. Chemical equilibrium can only be reached at high temperatures.
b. Chemical equilibrium can only be reached by starting with reactants.
c. At equilibrium, the reactant and product concentrations do not change with time.
d. At equilibrium, rate of the forward reaction is always greater than rate of the reverse reaction.
9. (6 pts) Identify each statement as true (T) or false (F) (circle your answer).
a) T
or
F
It is possible to have a negative value of K c.
b) T
or
F
Only aqueous substances are included in Kc expressions.
c) T
or
F
A large Kc value means the system is product-favored at equilibrium.
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Name: ______KEY______________________
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10. (7 pts) Write the equilibrium expression, Kc, for the following balanced equations.
CS2 (s) + 3Cl2 (g)  S2 Cl2 (g) + CCl4 (g)
Hg2+(aq) + 2Cl-(aq)  HgCl2 (s)
Kc = [S2 Cl2 ][CCl4 ] / [Cl2 ]3
Kc = 1 / [Hg2+][Cl-]2
11. (5 pts) Consider the reaction N2 (g) + 3H2 (g)  2NH3 (g) at 300 K. At equilibrium, the mixture
contains 0.10 M N 2 , 0.14 M H2 , and 0.20 M NH3 , in a closed flask. What is the value of Kc?
Kc = [NH3 ]2 / [N2 ][H2 ]3 = (0.20)2 / [ 0.10 M x (0.14 M)3 ]  Kc = 150
__E__ 12. (3 pts) The equilibrium constant at 300 K for the reaction: H2 (g) + Br2 (g)  2HBr(g) is 546.
What is the value of K’ for the reverse reaction (2HBr(g)  H2 (g) + Br2 (g))?
a. –546
b. 0.546
c. 546
d. 1.83x103
e. 0.00183
__A__ 13. (3 pts) The Kc for the formation of HBr from elemental bromine and hydrogen is 546 at 300
K. When [HBr] = 4.23 M, [H2 ] = 0.34 M, and [Br2 ] = 0.85 M, which statement below is correct?
a. Q = 61.9 which is less than Kc, the reaction needs to shift to the right to reach equilibrium
b. Q = 14.6 which is less than Kc, the reaction needs to shift to the right to reach equilibrium
c. Q = 0.0162 which is less than Kc, the reaction needs to shift to the right to reach equilibrium
d. There is not enough information to determine.
14. (10 pts) A closed flask initially contains 0.16 M C2 H6 (g) and 0.16 M Cl2 (g). The reaction (given
below) has an equilibrium constant, Kc, of 0.18 at 550o C. Calculate all equilibrium concentrations.
C2 H6 (g) + Cl2 (g)
 C2 H5 Cl(g) + HCl(g)
I 0.16 M
0.16 M
0
0
C
-x
-x
+x
+x
E 0.16 – x
0.16 – x
x
x
Kc = [C2 H5 Cl][HCl] / [C2 H6 ][Cl2 ] = x2 / (0.16 – x)2 = 0.18 (perfect squares)
x / (0.16 – x) = 0.42426
1.42426x = 0.06788
x = 0.42426 (0.16 – x)
x = 0.04766 M
x = 0.06788 – 0.42426x
[C2 H6 ]e q = [Cl2 ]e q = 0.16 – 0.04766 = 0.11 M; [C2 H5 Cl]e q = [HCl]e q = 0.048 M
15. (10 pts) For the reaction 2SO3 (g)  2SO2 (g) + O2 (g), ∆Η = +198 kJ carried out 25o C, determine in
which direction equilibrium will shift when the following changes are made:
a. [SO 2 ] increased ___left ()_____
b. Temperature decreased __left ()_____
c. Volume increased __right ()___
d. [O 2 ] decreased __right ()____
e. Catalyst is added __no change___
CHM 152, Fall 2016
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