Name ____________________________________ General Chemistry II
Sample Exam
Chapter 14 Sample Problems
1. In the reaction H2O2(aq) → H2O(l) + 0.5O2(g), the initial concentration of H2O2 is 0.2546 M, and the initial rate of
reaction is 9.32 10-4 M s-1. What will be [H2O2] at t = 35 s?
2. For the gas phase decomposition of hydrogen iodide at 700 K 2 HI(g) →H2(g) + I2(g) the average rate of disappearance
of HI over the time period from t = 0 s to t = 797 s is found to be 5.28 x 10-4 M/s. What is the average rate of appearance
of H2 over the same time period?
3. A reaction has the rate law Rate = k[A][B]2. What is the order of the reaction?
4. In the first-order decomposition of dinitrogen pentoxide at 335 K,
N2O5(g) → 2NO2(g) + 0.5O2(g)
if we start with a 2.50 g sample of N2O5 at 335 K and have 1.50 g remaining after 109 s, (a) What is the value of the
rate constant k? (b) What is the half-life of the reaction? (c) What mass of N2O5 will remain after 5.0 min?
5. The decomposition of hydrogen iodide on a gold surface at 150C: HI(g) ⇄ H2(g) + I2(g) is zero order in HI with a
rate constant of 1.20 x 10-4 Ms-1. If the initial concentration of HI is 0.110 M, what is the concentration of HI after
776 seconds have passed
6. A general reaction is the formation of molecule C from two reactant molecules, A and B.
A + B → C
The reaction was run multiple times at constant temperature using different initial concentrations of the two reactants.
The initial rates obtained are included in the table below.
[A], mol/L [B], mol/L rate, mol/(L-min)
Trial 1 0.350 0.880 0.180
Trial 2 0.770 0.880 0.360
Trial 3 0.350 1.76 0.360
Trial 4 0.967 0.651 0.368
What is the reaction order with respect to A? What is the reaction order with respect to B? Determine the rate
equation and the value of the rate constant.
7. The rate of the reaction between CO and NO2 at 540 K
CO(g) + NO2(g) →CO2(g) + NO(g)
was measured starting with various concentrations of CO and NO2.
[CO], mol/L [NO2], mol/L rate, mol/(L-min)
Trial 1 5.10 x 10-4 3.50 x 10-5 3.4 x 10-8
Trial 2 5.10 x 10-4 7.00 x 10-5 6.8 x 10-8
Trial 3 5.10 x 10-4 1.75 x 10-5 1.7 x 10-8
Trial 4 1.02 x 10-3 3.50 x 10-5 6.8 x 10-8
Trial 5 1.53 x 10-3 3.50 x 10-5 10.2 x 10-8
What is the reaction order with respect to A? What is the reaction order with respect to B? Determine the rate
equation and the value of the rate constant.
8. Rate constants for the first-order decomposition of acetonedicarboxylic acid
CO(CH2COOH)2(aq) → CO(CH3)2(aq) + 2 CO2(g)
are k = 4.75 x 10-4 s-1 at 293 K and k = 1.63 x10-3 s-1 at 303 K. What is the activation energy, Ea, for this reaction?
9. The gas phase decomposition of hydrogen peroxide at 400 C
H2O2 (g) → H2O(g) + O2(g)
is second order in H2O2 with a rate constant of 0.650 M
-1 s-1. If the initial concentration of H2O2 is 0.118 M, the
concentration of H2O2 will be M after 56.7 seconds have passed.
10. In a study of the decomposition of ammonia on a platinum surface at 856 C
NH3 → 1/2 N2 + 3/2 H2
the concentration of NH3 was followed as a function of time.
It was found that a graph of [NH3] versus time in seconds gave a straight line with a slope of -2.15 x 10
-6 M s-1 and a
y-intercept of 2.38 x 10-3 M.
Based on this plot, determine the reaction order for NH3 and the rate constant for the reaction in M s
-1.
11. In a study of the decomposition of ammonia on a tungsten surface at 1100 C
NH3 → 1/2 N2 + 3/2 H2
the following data were obtained:
[NH3], M 7.05 x 10
-3 3.53 x 10-3 1.77 x 10-3 8.85 x 10-4
seconds 0 441 661 772
Hint: It is not necessary to graph these data.
a. The observed half life for this reaction when the starting concentration is 7.05x 10-3 M is ___________________
s and when the starting concentration is 3.53 x 10-3 M is ___________________ s.
b. The average rate of disappearance of NH3 from t = 0 s to t = 441 s is ___________________ M s
-1.
c. The average rate of disappearance of NH3 from t = 441 s to t = 661 s is ___________________ M s
-1.
d. Based on these data, the rate constant for this order reaction is ___________________ M s-1.
12. The following mechanism for the gas phase reaction of H2 and ICl that is consistent with the observed rate law is:
step 1 slow: H2(g) + ICl(g) → HCl(g) + HI(g)
step 2 fast: ICl(g) + HI(g) → HCl(g) + I2(g)
a. What is the equation for the overall reaction? Use the smallest integer coefficients possible.
b. Which species acts as a catalyst? Enter formula. If none, write none:
c. Which species acts as a reaction intermediate? Enter formula. If none, write none:
d. Complete the rate law for the overall reaction that is consistent with this mechanism.
Rate =
13. A student proposed the following mechanism for the gas phase reaction of fluorine with chlorine dioxide.
step 1 fast: 2 ClO2 → Cl2O4
step 2 slow: Cl2O4 + F2 → 2 FClO2
a. What is the equation for the overall reaction? Use the smallest integer coefficients possible.
b. Which species acts as a catalyst? Enter formula. If none, write none:
c. Which species acts as a reaction intermediate? Enter formula. If none, write none:
d. Complete the rate law for the overall reaction that is consistent with this mechanism.
Rate =
Chapter 15 Sample Problems
14. Write the equilibrium-constant expression for the following reaction.
CO2 (g) + 2H2 (g) ⇄ CH3OH (g)
15. Given the following: I) 2NO(g) ⇄ N2O(g) + 1/2 O2(g) Kc = 5.9 x 10
12 II) N2(g) + O2(g) ⇄ 2NO(g) Kc = 4.1 x 10
-31
Find the value of the equilibrium constant for the following equilibrium reaction: N2(g) + 1/2 O2(g) ⇄ N2O(g)
16. Which of the following expressions is the correct equilibrium-constant expression for the reaction below?Write the
equilibrium-constant expression for the following reaction. CO2 (s) + H2O (l) ⇄ H
+ (aq) + HCO-3 (aq)
17. For the reaction: 2 SO2(g) + O2(g) ⇄ 2 SO3(g), Kc = 6.9 x 10
24 at 25 C. If a reaction vessel is filled with these gases,
such that [SO2] = 6.0 M, [O2] = 6.0 M and [SO3] = 6.0 M, what is the reaction quotient? In which direction will the
reaction proceed?
18. Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution:
HC2H3O2 (aq) ⇄ C2H3O
-
2 (aq) + H
+ (aq)
At equilibrium at 25 C a 0.100 M solution of acetic acid has the following concentrations: [HC2H3O2] = 0.0990 M,
[C2H3O
-
2] = 1.33 x 10
-3 M and [H+] = 1.33 x 10-3 M.
a. Find the equilibrium constant,
b. Does this equilibria favor reactants or products?
19. A mixture, containing 0.0750 M HCl(g) and 0.0330 M O2(g) is allowed to come to equilibrium at 480C.
4HCl(g) + O2(g) ⇄ 2Cl2(g) + 2H2O(g)
At equilibrium [Cl2] = 0.030 M. What is the value of Kc?
20. The water-gas shift reaction is important in several chemical processes, such as the production of H2 for fuel cells.
This reaction can be written as follows:
H2(g) + CO2(g) ⇄ H2O(g) + CO (g)
K = 0.106 at 700 K. If a mixture of gases that initially contains 0.0150 M H2 and 0.0150 M CO2 is allowed to equilibrate
at 700 K, what are the final concentrations of all substances present?
21. Consider the following reaction where Kc = 1.29 x 10
-2 at 600 K.
COCl2(g) ⇄ CO(g) + Cl2(g)
A reaction mixture was found to contain 0.127 moles of COCl2(g), 5.17 x 10
-2 moles of CO(g), and 4.24 x 10-2 moles
of Cl2(g), in a 1.00 liter container.
Is the reaction at equilibrium? If not, what direction must it run in order to reach equilibrium?
Hint, calculate the reaction quotient, Qc.
22. Consider the following reaction where Kc = 1.80 x 10
-4 at 298 K.
NH4HS(s) ⇄ NH3(g) + H2S(g)
A reaction mixture was found to contain 5.46 x 10-2 moles of NH4HS(s), 8.16 x 10
-3 moles of NH3(g), and 1.34 x
10-2 moles of H2S(g), in a 1.00 liter container.
Is the reaction at equilibrium? If not, what direction must it run in order to reach equilibrium?
Hint, calculate the reaction quotient, Qc.
23. The equilibrium constant, Kc, for the following reaction is 5.10 x 10
-6 at 548 K.
NH4Cl(s) ⇄ NH3(g) + HCl(g)
If an equilibrium mixture of the three compounds in a 6.31 L container at 548 K contains 3.52 mol of NH4Cl(s) and
0.497 mol of NH3, calculate the number of moles of HCl present.
24. A student ran the following reaction in the laboratory at 607 K:
CO(g) + Cl2(g) ⇄ COCl2(g)
When she introduced 0.201 moles of CO(g) and 0.233 moles of Cl2(g) into a 1.00 liter container, she found the
equilibrium concentration of COCl2(g) to be 0.163 M.
Calculate the equilibrium constant, Kc, she obtained for this reaction.
25. The equilibrium constant, Kc, for the following reaction is 9.52 x 10
-2 at 350 K.
CH4 (g) + CCl4 (g) ⇄ 2 CH2Cl2 (g)
Calculate the equilibrium concentrations of reactants and product when 0.369 moles of CH4 and 0.369 moles of
CCl4 are introduced into a 1.00 L vessel at 350 K.
