1022_1st Exam_1030319
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Hydrogen iodide decomposes at 800 K via a second-order process to produce hydrogen and iodine according to the following chemical equation.
2HI(g) H2(g) + I2(g)
At 800 K it takes 142 seconds for the initial concentration of HI to decrease from 6.75 × 10-2 M to 3.50 × 10-2 M.
What is the rate constant for the reaction at this temperature?
A) 5.12 × 10-4 M-1s-1 B) 9.69 × 10-2 M-1s-1
C) 10.3 M-1s-1 D) 1.95 × 103 M-1s-1
Answer: B
2) Cyclohexane (C6H12) undergoes a molecular rearrangement in the presence of AlCl3 to form methylcyclopentane (MCP) according to the equation:
C6H12 MCP
If Kc = 0.143 at 25°C for this reaction, predict the direction in which the system will shift if the initial concentrations of C6H12 and MCP are 0.0400 M and 0.0200 M, respectively. The system
A) will shift right.
B) is already at equilibrium.
C) is not at equilibrium and will remain in an unequilibrated state.
D) will shift left.
Answer: D
3) Consider the following reaction at equilibrium. What effect will adding 1 mole of Ar to the reaction mixture have on the system?
2 H2S(g) + 3 O2(g) 2 H2O(g) + 2 SO2(g) A) The reaction will shift to the left in the direction of reactants.
B) No effect will be observed.
C) The equilibrium constant will increase.
D) The reaction will shift to the right in the direction of products.
E) The equilibrium constant will decrease.
Answer: B
4) A reaction is found to have an activation energy of 38.0 kJ/mol. If the rate constant for this reaction is 1.60 × 102 M-1s-1 at 249 K, what is the rate constant at 436 K?
A) 7.94 × 104 M-1s-1 B) 2.38 × 105 M-1s-1 C) 1.26 × 103 M-1s-1 D) 3.80 × 104 M-1s-1 E) 4.20 × 105 M-1s-1 Answer: E
5) Which of the following statements is TRUE?
A) The addition of a homogeneous catalyst does not change the activation energy of a given reaction.
B) The rate constant does not depend on the activation energy for a reaction where the products are lower in energy than the reactants.
C) A catalyst raises the activation energy of a reaction.
D) Rate constants are temperature dependent.
E) None of the above are true.
Answer: D
6) Determine the value of Kc for the following reaction if the equilibrium concentrations are as follows: [PBr5]eq = 0.56 M, [PBr3]eq = 0.23 M, [Br2]eq = 3.3 M.
PBr5(g) PBr3(g) + Br2(g)
A) 1.4 B) 0.74 C) 0.93 D) 0.76 E) 1.1
Answer: A
7) The decomposition of N2O5 in solution in carbon tetrachloride proceeds via the reaction 2N2O5 (soln) 4NO2 (soln) + O2 (soln)
The reaction is first order and has a rate constant of 4.82 × 10-3 s-1 at 64°C. If the reaction is initiated with 0.058 mol in a 1.00-L vessel, how many moles remain after 151 s?
A) 0.055 M B) 2.0 × 103 M C) 0.028 M D) 0.060 M E) 12 M
Answer: C
8) Identify the rate-determining step.
A) the slowest step B) always the last step C) always the second step D) the faster step
E) the fast step Answer: A
9) Cyclohexane, C6H12, undergoes a molecular rearrangement in the presence of AlCl3 to form methylcyclopentane, CH3C5H9, according to the equation:
C6H12 CH3C5H9
If Kc = 0.143 at 25°C for this reaction, find the equilibrium concentrations of C6H12 and CH3C5H9 if the initial concentrations are 0.200 M and 0.075 M, respectively.
A)[C6H12] = 0.041 M, [CH3C5H9] = 0.041 M B)[C6H12] = 0.241 M, [CH3C5H9] = 0.034 M C)[C6H12] = 0.253 M, [CH3C5H9] = 0.022 M D)[C6H12] = 0.159 M, [CH3C5H9] = 0.116 M Answer: B
10) In a reaction mixture containing reactants and products, each at a concentration of 1M, what is the value of Q?
A) 0 B) 1 C) D) -1
E) It cannot be determined without concentrations.
Answer: B
11) Given the following rate law, how does the rate of reaction change if the concentration of X is doubled?
Rate = k [X][Y]2
A) The rate of reaction will increase by a factor of 3.
B) The rate of reaction will increase by a factor of 5.
C) The rate of reaction will increase by a factor of 2.
D) The rate of reaction will decrease by a factor of 2.
E) The rate of reaction will remain unchanged.
Answer: C
12) Carbon-14 has a half-life of 5720 years and this is a first order reaction. If a piece of wood has converted 75%
of the carbon-14, then how old is it?
A) 1430 years B) 2375 years C) 11440 years D) 4290 years E) 4750 years Answer: C
13) A particular first-order reaction has a rate constant of 1.35 × 102 s-1 at 25.0°C. What is the magnitude of k at 75.0°C if Ea = 85.6 kJ/mol?
A) 1.92 × 104 s-1 B) 3.47 × 104 s-1 C) 3.85 × 106 s-1 D) 670 s-1
E) 1.36 × 102 s-1 Answer: A
14) Consider the following reaction:
CH4(g) + 2 H2S(g) CS2(g) + 4 H2(g)
A reaction mixture initially contains 0.50 M CH4 and 0.75 M H2S. If the equilibrium concentration of H2 is 0.44 M, find the equilibrium constant (Kc) for the reaction.
A) 0.038 B) 2.9 C) 0.23 D) 0.34 E) 10.
Answer: A
15) Determine the value of Kp for the following reaction if the equilibrium concentrations are as follows: P(CO)eq = 6.8 × 10-11 atm, P(O2)eq = 1.3 × 10-3 atm, P(CO2)eq = 0.041 atm.
2 CO(g) + O2(g) 2 CO2(g)
A) 3.6 × 10-21 B) 2.8 × 1020 C) 4.6 × 1011 D) 2.2 × 10-12 E) 3.6 × 10-15
16) What are the units of k in a second order reaction?
A) M-1s-1 B) M C) 1M D) Ms E) M2
s Answer: A
17)What is n for the following equation in relating Kc to Kp?
CH4(g) + H2O(g) CO(g) + 3 H2(g)
A) 2 B) -2 C) -1 D) 0 E) -3
Answer: A
18) Express the equilibrium constant for the following reaction.
4PCl5(g) 4PCl3(g) + 4Cl2(g) A) K = [PCl5]4
[PCl3]4[Cl2]4 B) K =[PCl3]2[Cl2]2
[PCl5]2 C) K =[PCl3][Cl]2
[PCl5]
D) K = [PCl5]1/2 [PCl3]1/2[Cl2]1/2 E) K =[PCl3]4[Cl2]4
[PCl5]4 Answer: E
19) What is the overall order of the following reaction, given the rate law?
NO(g) + O3(g) NO2(g) + O2(g) Rate = k[NO][O3]
A) 3rd order B) 0th order C) 1st order D) 1 12 order E) 2nd order
Answer: E
20) Identify an homogeneous catalyst.
A)H2SO4 with concentrated HCl B)N2 and H2 catalyzed by Fe C) Pt with methane
D)Pd in H2 gas
E)SO2 over vanadium (V) oxide Answer: A
21) Give the direction of the reaction, if K >> 1.
A) The forward reaction is favored.
B) If the temperature is raised, then the reverse reaction is favored.
C) If the temperature is raised, then the forward reaction is favored.
D) Neither direction is favored.
E) The reverse reaction is favored.
Answer: A
22)Consider the following reaction and its equilibrium constant:
SO2(g) + NO2(g) SO3(g) + NO(g) Kc = 0.33
A reaction mixture contains 0.41 M SO2, 0.14 M NO2, 0.12 M SO3 and 0.14 M NO. Which of the following statements is TRUE concerning this system?
A) The reaction quotient will decrease.
B) The equilibrium constant will decrease.
C) The reaction will shift in the direction of products.
D) The reaction will shift in the direction of reactants.
E) The system is at equilibrium.
Answer: C
23) The Kp for the reaction below is 1.49 × 108 at 100.0°C:
CO(g) + Cl2(g) COCl2(g)
In an equilibrium mixture of the three gases, PCO = PCl2 = 2.22 × 10-4 atm. The partial pressure of the product, phosgene (COCl2), is ________ atm.
A) 6.67 × 1011 B) 7.34 C) 3.02 × 1015 D) 3.31 × 10-16 E) 3.31 × 104 Answer: B
24)What is n for the following equation in relating Kc to Kp?
SO3(g) + NO(g) SO2(g) + NO2(g)
A) -1 B) 2 C) 0 D) -2 E) 1
Answer: C
25)The equilibrium constant is given for one of the reactions below. Determine the value of the missing equilibrium constant.
H2(g) + Br2(g) 2 HBr(g) Kc = 3.8 × 104 4 HBr(g) 2 H2(g) + 2 Br2(g) Kc = ?
A) 1.6 × 103 B) 6.9 × 10-10 C) 5.1 × 10-3 D) 1.9 × 104 E) 2.6 × 10-5 Answer: B
26) The equilibrium constant is given for two of the reactions below. Determine the value of the missing equilibrium constant.
2A(g) + B(g) A2B(g) Kc = ? A2B(g) + B(g) A2B2(g) Kc = 16.4 2A(g) + 2B(g) A2B2(g) Kc = 28.2
A) 462 B) 0.00216 C) 1.72 D) 11.8 E) 0.582
Answer: C
27) A particular first-order reaction has a rate constant of 1.35 × 102 s-1 at 25.0°C. What is the magnitude of k at 95.0°C if Ea = 55.5 kJ/mol?
A) 576 s-1 B) 2.85 × 104 s-1 C) 9.56 × 103 s-1 D) 4.33 × 1087 s-1
E) 1.36 × 102 s-1 Answer: C
28) Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures according to the equation:
PCl5(g) PCl3(g) + Cl2(g)
At 250° 0.125 M PCl5 is added to the flask. If Kc = 1.80, what are the equilibrium concentrations of each gas?
A)[PCl5] = 3.96 M, [PCl3] = 3.83 M, and [Cl2] = 3.83 M B)[PCl5] = 0.00765 M, [PCl3] = 0.117 M, and [Cl2] = 0.117 M C)[PCl5] = 1.80 M, [PCl3] = 1.80 M, and [Cl2] = 1.80 M D)[PCl5] = 0.0625 M, [PCl3] = 0.335 M, and [Cl2] = 0.335 M Answer: B
29)In which of the following reactions will Kc = Kp?
A)SO3(g) + NO(g) SO2(g) + NO2(g) B)2 N2(g) + O2(g) 2 N2O(g)
C)4 NH3(g) + 3 O2(g) 2 N2(g) + 6 H2O(g) D)2 SO2(g) + O2(g) 2 SO3(g)
E)None of the above reactions have Kc = Kp.
Answer: A
30) Express the equilibrium constant for the following reaction.
NaClO3(s) NaClO(s) + O2(g) A) K =[NaClO]2[O2]2
[ NaClO3]2 B) K = [O2]-1 C)K = [O2]
D) K =[NaClO][O2]
[ NaClO3]
E) K = [ NaClO3]
[NaClO][O2]
Answer: C
31) Given the following proposed mechanism, predict the rate law for the overall reaction.
2NO2 + Cl2 2NO2Cl (overall reaction) Mechanism
NO2 + Cl2 NO2Cl + Cl slow
NO2 + Cl NO2Cl fast
A)Rate = k[NO2][Cl]
B) Rate = k[NO2Cl][Cl]2 C) Rate = k[NO2Cl]2 D)Rate = k[NO2][Cl2]
E) Rate = k[NO2]2[Cl2]2 Answer: D
32) Given the following balanced equation, determine the rate of reaction with respect to [NOCl].
2 NO(g) + Cl2(g) 2 NOCl(g) A) Rate = + 12 [NOCl]
t B) Rate = - 12 [NOCl]
t C) Rate = - 2 [NOCl]t D) Rate = - 12 [NO]
t
E) It is not possible to determine without more information.
Answer: A
33) Determine the rate law and the value of k for the following reaction using the data provided.
S2O82 (aq) + 3 I (aq) 2 SO42 (g) + I3 (aq) [S2O82 ]i (M) [I ]i (M) Initial Rate (M-1s-1)
0.30 0.42 4.54
0.44 0.42 6.65
0.44 0.21 3.33
A) Rate = 36 M-1s-1 [S2O82 ][I ] B) Rate = 120 M-2s-1 [S2O82 ]2[I ] C) Rate = 23 M-1/2s-1 [S2O82 ][I ]1/2 D) Rate = 86 M-2s-1 [S2O82 ][I ]2
E) Rate = 195 M-3s-1 [S2O82 ]2[I ]2 Answer: A
34) The equilibrium constant is equal to 5.00 at 1300 K for the reaction:
2 SO2(g) + O2(g) 2 SO3(g).
If initial concentrations are [SO2] = 6.00 M, [O2] = 0.45 M, and [SO3] = 9.00 M, the system is A) not at equilibrium and will remain in an unequilibrated state.
B) not at equilibrium and will shift to the left to achieve an equilibrium state.
C) at equilibrium.
D) not at equilibrium and will shift to the right to achieve an equilibrium state.
Answer: C
35) Consider the following reaction:
2 H2O(g) + 2 SO2(g) 2 H2S(g) + 3 O2(g)
A reaction mixture initially contains 2.8 M H2O and 2.6 M SO2. Determine the equilibrium concentration of H2S if Kc for the reaction at this temperature is 1.3 × 10-6.
A) 0.058 M B) 0.028 M C) 0.12 M D) 3.1 × 10-3 M E) 0.045 M
Answer: C
36)Calculate the value of [N2]eq if [H2]eq = 2.0 M, [NH3]eq = 0.5 M, and Kc = 2.
N2(g) + 3 H2(g) 2 NH3(g)
A) 0.016 M B) 0.031 M C) 62.5 M D) 0.062 M E) 0.40 M
Answer: A
37)What is n for the following equation in relating Kc to Kp?
4 NH3(g) + 3 O2(g) 2 N2(g) + 6 H2O(g)
A) 3 B) 2 C) -2 D) 1 E) -1
Answer: D
38) The first-order decay of radon has a half-life of 3.823 days. How many grams of radon remain after 7.22 days if the sample initially weighs 250.0 grams?
A) 54.8 g B) 4.21 g C) 183 g D) 76.3 g E) 67.5 g
Answer: E
39)Given the following balanced equation, determine the rate of reaction with respect to [O2].
2 O3(g) 3 O2(g) A) Rate = + 2 [O2]
t B) Rate = - 23 [O2]
t C) Rate = - 3 [O2]
t D) Rate = + 13 [O2]
∆t
E) It is not possible to determine without more information.
Answer: D
40) Nitrogen dioxide decomposes at 300°C via a second-order process to produce nitrogen monoxide and oxygen according to the following chemical equation.
2 NO2(g) 2 NO(g) + O2(g).
A sample of NO2(g) is initially placed in a 2.50-L reaction vessel at 300°C. If the half-life and the rate constant at 300°C are 11 seconds and 0.54 M-1 s-1, respectively, how many moles of NO2 were in the original sample?
A) 5.9 mol B) 0.42 mol C) 0.17 mol D) 15 mol
Answer: B
