BINGHAMTON UNIVERSITY (SUNY) DEPARTMENT OF CHEMISTRY VERSION A (ANSWER KEY)
CHEM 111 – Chemical Principles (Fall 2012) Exam 3 Nov. 28, 2012
Time: 90
... [Show More] minutes (1 hr 30 minutes); Answer all questions
1. Which of the following is/are expected to affect the rate of a chemical reaction?
a. Increasing the reaction temperature
b. Decreasing the reactant concentrations
c. Doubling the volume of the reaction container
A) A only
B) B only
C) C only
D) A and B
2. For the reaction
IO3–(aq) + 5I–(aq) + 6H+(aq) 3I2(aq) + 3H2O(l)
the rate of disappearance of I–(aq) at a particular time and concentration is 2.6 10– 3 mol/(L • s). What is the rate of appearance of I2(aq)?
A) 1.6 10–3 mol/(L • s)
B) –1.6 10–3 mol/(L • s)
C) 7.8 10–3 mol/(L • s)
D) 4.3 10–3 mol/(L • s)
3. For the reaction
2N2O5(g) 4NO2(g) + O2(g)
which of the following expressions is equal to the rate of the reaction? A)
B)
C)
D)
4. For the hypothetical reaction A + 2B 2C + D, the initial rate of disappearance of A is
2.0 x 10–2 mol/(L • s). What is the initial rate of disappearance of B? A) 1.4 x10–1 mol/(L • s)
B) 4.0 x10–4 mol/(L • s)
C) 4.0 x 10–2 mol/(L • s)
D) 1.4 x10–2 mol/(L • s)
5. The reaction
2H2(g) + 2NO(g) 2H2O(g) + N2(g)
is first-order in H2 and second-order in NO at a particular temperature. What is the rate law?
A) Rate = k[H2]2[NO]2
B) Rate = k[H2][NO]2
C) Rate = k[H2][NO]
D) Rate = k[H2O]2[N2]
6. The following data were obtained for the hypothetical reaction A + B products.
[A]0 (M) [B]0 (M) Initial Rate (M/s)
0.2 0.1 5
0.2 0.2 20
0.6 0.1 15
What is the overall order of this reaction?
A) 3 B)1/2
C) 2
D) 4
7. Which of the following corresponds to the correct integrated expression for a second- order reaction?
A)
B)
C)
D)
8. The nuclide 96Nb decays by a first-order process with a rate constant of 2.96 10–2 h–1. How long will it take for 82.0% of the initial amount of 96Nb to be consumed?
A) 33.8 h
B) 57.9 h
C) 27.7 h
D) 6.70 h
9. The potential-energy diagram below describes the hypothetical reaction A + B C + D. Assuming the y-axis label refers to the enthalpy (H) per mol, which of the following statements concerning this reaction coordinate is/are correct?
1. The forward reaction is exothermic.
2. The forward reaction rate is proportional to the change in enthalpy (H) of the forward reaction.
3. Ea(forward) Ea(reverse) is equal to the change in enthalpy (H) of the forward reaction.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
10. For the reaction Br2(g) + Cl2(g) 2BrCl(g), at equilibrium, it is found that the concentrations of Br2, Cl2, and BrCl are 0.398 M, 0.351 M, and 2.05 10–3 M, respectively. What is the value of Kc?
A) 3.01 10–5
B) 1.20 10–4
C) 1.47 10–2
D) 6.81 101
11. Which of the following pairs of species is not a conjugate acid–base pair?
A) HOCl, OCl–
B) HNO2, NO2+
C) HSO4–, SO 2–
D) H2CO3, HCO –
12. In a chemical reaction at constant temperature, the addition of a catalyst
A) provides an alternative reaction pathway thus lowering the activation energy.
B) increases the concentration of the products at equilibrium.
C) affects the equilibrium constant.
D) increases the fraction of molecules with more than a given kinetic energy.
13. When gaseous carbon monoxide and hydrogen are combined in a sealed vessel and heated they will eventually form an equilibrium mixture of reactants and products according to the balanced chemical equilibrium below.
CO(g) + 3H2(g) CH4(g) + H2O(g)
In one such reaction 3 moles of H2 gas were combined with 1 mole of CO gas in a fixed volume vessel and heated to 1200 K. Analysis of the reaction mixture at various times gave the results below. Which component of the reaction mixture is represented by curve B?
A) carbon monoxide
B) hydrogen
C) either methane or water
D) either hydrogen or carbon monoxide
14. Carbon tetrachloride may react with oxygen to produce chlorine and carbonyl chloride. 2CCl4(g) + O2(g) 2COCl2(g) + 2Cl2(g); Kc = 9.9 1051
What is Kc for the following equilibrium?
COCl2(g) + Cl2(g) CCl4(g) + ½O2(g) A) 9.9 10–51
B) 5.0 10–53
C) 1.0 10–52
D) 1.0 10–26
15. Consider the reaction NH3(aq) + H2O(l) NH4+(aq) + OH–(aq). Kb for NH3 is
1.8 10–5 at 25°C. What is Ka for the NH4+ ion at 25°C? A) 5.6 104
B) 5.6 10–10
C) 1.8 10–5
D) 7.2 10–12 [Show Less]