Exam_980318
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Consider the reaction profile shown above. The point labelled B refers to the A) activation energy.
B) products.
C) reactants.
D) catalyst.
E) activated complex.
Answer: E
2) Consider the reaction profile shown above. The activation energy of the reaction is represented by the difference in energy between points
A) C and D. B) B and C. C) A and B. D) A and D. E) A and C.
Answer: C
3) Consider the reaction profile shown above. Is the reaction endothermic or exothermic, and why?
A) Endothermic, because the reaction must possess a large amount of energy in order to go from A B.
B) Endothermic, because the reaction at point A possesses more energy than the reaction at point D.
C) Exothermic, because the transition state (B) is much higher in energy than the products (D).
D) Exothermic, because the difference in energy between point A and point D is a negative value.
E) The reaction profile doesn't indicate whether a reaction is endothermic or exothermic.
Answer: D
4) Consider the reaction profile shown above. Addition of a catalyst to the reaction will cause A) the difference in energy between point A and B to decrease.
B) the energy of point D to increase.
C) the energy of point C to increase.
D) the difference in energy between point A and D to decrease.
E) the energy of point A to decrease.
Answer: A
5) An equilibrium mixture of NO (g), O2 (g) and NO2 (g) is allowed to expand from 1.0 L to 2.0 L at a constant temperature.
2 NO (g) + O2 (g) 2 NO2 (g) Which of the following statements is correct?
A) The value of Kp would decrease.
B) Concentration of all three gases are unchanged.
C) The number of moles of all three gases are unchanged.
D) The number of moles of O2 would increase.
E) The number of moles of NO2 would increase.
Answer: D
6) The reaction of O3 with Cl· is believed to occur by the mechanism shown below.
O3 + Cl· ClO· + O2 ClO· + O Cl· + O2 In this mechanism, Cl· is
A) an intermediate.
B) the activated complex.
C) a reactant in the overall reaction.
D) a product of the overall reaction.
E) the catalyst.
Answer: E
7) At some point during a reaction, the following concentrations are measured.
2 ICl (g) I2 (g) + Cl2(g) Kc = 8.33 ×10-4 0.15 M 0.00125 M 0.0075 M
Which of the following represents a true statement?
A) The reaction will proceed until all ICl is consumed.
B) The concentration of Cl2 will increase in reaching equilibrium.
C) The reaction is at equilibrium.
D) I2 will be consumed in reaching equilibrium.
Answer: B
8) In the plot of ln(k) versus 1/T for a first order reaction, the frequency factor (A) can be determined by A) the intercept on the y-axis.
B) the slope of the line times R.
C) the intercept of the x-axis.
D) the slope of the line.
E) the negative of the slope of the line times R.
Answer: A
9) For first order reactions the slope of a plot of ln [A] vs. time is
A) k ln [A] 0. B) -k. C) kt. D) k. E) k/t.
Answer: B
10) Based on a reaction profile, the energy of activation for the forward reaction is 411 kJ and the enrgy of activation for the backward reaction is 169 kJ. What is the enthalpy of reaction?
A) -242 B) 0.411 C) 242 D) 580 E) 2.43
Answer: C
11) If 0.22 atm H2S(g) are added to a 1.0 L flask containing an excess of I2(s), what will be the equilibrium concentration of HI? (note: equation unbalanced)
H2S (g) + I2 (s) HI (g) + S (s) Kp = 1.34 × 10-5 at 60°C A) 3.0 × 10-6 atm
B) 6.9 × 10-3 atm C) 8.6 × 10-4 atm D) 1.7 × 10-3 atm
E) More information is needed to answer this question.
Answer: D
12) At equilibrium in the following reaction at 319 K, the concentration of NO2 (g) is 2.09 M. What is the concentration of N2O4 (g) if the equilbrium constant for this reaction is determined to be 39.68 at 319K?
2 NO2 (g) N2O4 (g)
A) 362 B) 19.0 C) 82.9 D) 173 E) 0.110
Answer: D
13) Balance the following equation and determine the equilibrium constant expression, Kc.
C (s) + H2O (g) C2H5OH (g) + O2 (g) (not balanced) A) C2H5OH O2
H2O
B) C H2O
C 2 H2O 3 C) [C2H5OH] [O2]
D) C2H5OH O2 C H2O E) C2H5OH O2
H2O 3 Answer: E
14) What is the value of Q for the following reaction if [HI] = 0.16 M, [H2] = 0.899 M, and [I2] = 0.90 M?
H2 + I2 2 HI
A) 2.5 B) 5.1 C) 0.32 D) 0.40 E) 0.032
Answer: E
15) A mixture is prepared with [CO] = 0.035, [Cl2] = 0.015, and [COCl2] = 0.95. It is known that Kc for the equilibrium CO (g) + Cl2 (g) COCl2 (g) is 1.2 × 103 at 400°C. Predict what will happen.
A) The reaction occurs in the forward direction.
B) The reaction is at equilibrium so no net reaction occurs.
C) The reaction occurs in the reverse direction.
D) It is impossible to predict without more information.
Answer: C
16) Without doing detailed calculations, estimate the length of time required for the following reaction to have used up all but 25% of the starting material.
H2 + C2H4 C2H6 t1/2 = 2.5 minutes
A) 5.0 minutes B) 2.5 minutes C) 7.5 minutes D) 100 minutes E) 0.6 minutes Answer: A
Two mechanisms proposed for the following reaction of nitrogen dioxide with carbon monoxide are shown below. Use this information to answer the following questions.
NO2 (g) + CO CO2 (g) + NO (g)
Mechanism I: NO2 (g) + CO CO2 (g) + NO (g) (one step) Mechanism II: NO2 (g) + NO2 (g) NO3 (g) + NO (g) (slow) NO3 (g) + CO (g) CO2 (g) + NO2 (g) (fast)
Figure 1
17) Refer to the information in Figure 1. What is the predicted rate law for Mechanism I?
A) rate = k[NO2]
B) rate = k[NO2] 2 C) rate = k[NO2] 2[CO]
D) rate = k[NO2] [CO]
E) rate = k[NO][CO2]
Answer: D
18) Refer to the information in Figure 1. What is the predicted rate law for Mechanism II?
A) rate = k[NO3][CO]
B) rate = k[NO2] 2 C) rate = k[NO2][CO]
D) rate = k[NO2]
E) rate = k[NO2] 2[CO]
Answer: B
19) Refer to the information in Figure 1. If the activation energy for the forward reaction is greater than the activation energy for the reverse reaction, the reaction is
A) exothermic.
B) endothermic.
C) faster in the forward direction.
D) faster in the reverse direction.
E) spontaneous.
Answer: B
20) Refer to the information in Figure 1. The experimental rate law is found to be: rate = k[NO2] 2. Which (if any) mechanism is consistent with this rate law?
A) Mechanism II B) Mechanism I
C) Neither mechanism is consistent with this rate law.
Answer: A
21) What is the equilibrium constant if [A] = 0.01M, [B] =0.90M, [C] = 0.70M in the presence of 0.50M D?
2A (aq) B (aq) + C (aq)+ D (s)
A) 6300 B) 130 C) 0.016 D) 3150 E) 450
Answer: A
22) How many of the following factors affect the numerical value of the equilibrium constant K?
pressure initial concentration
volume temperature
chemical equation
A) 0 B) 1 C) 2 D) 3 E) 4
Answer: C
23) Which direction will the following reaction (in a 5.0 L flask) proceed if more calcium oxide is added to the system?
CaCO3 (s) CaO (s) + CO2 (g) Kp = 1.9 × 10-23 A) to the right
B) to the left
C) The equilibrium constant gets smaller to reflect the added calcium oxide.
D) The equilibrium position will not shift because calcium oxide is a solid.
E) More information is needed to answer this question.
Answer: D
24) The decomposition of N2O on a platinum surface is found to be zero order with a rate 2 N2O (g) 2 N2 (g) + O2 (g)
constant, k = 1.48 × 10-3 M s-1. If the initial concentration of N2O is 0.240 M, what would be the half-life for the reaction, in s?
A) 13.0 B) 36.4 C) 52.4 D) 128 E) 81.1
Answer: E
25) The rate constant for a particular reaction is 2.7 × 10-2s-1 at 25°C and 6.2 × 10-2s-1 at 115°C. What is the activation energy for the reaction, in kJ/mol?
A) 87 B) 0.089 C) 8.9 D) 0.0045 E) 13
Answer: C
26) Consider the following exothermic reaction:
N2 (g) + 3 H2 (g) 2 NH3 (g)
Which of the following changes would not increase the amount of NH3 produced from given quantities of N2 and H2?
A) an increase in T B) an increase in P C) a decrease in V
D) removing some NH3 and reestablishing equilibrium E) none of the above
Answer: A
27) Which is not correct concerning equilibrium?
A) The rates of the forward and reverse reactions are the same.
B) At equilibrium, the rates of the forward and reverse reaction become zero.
C) Either the reactants or the products of a reaction could be used to attain equilibrium for a reversible reaction.
D) The ratio of the concentrations of products and reactants, raised to appropriate powers, is a constant.
E) The concentration of reactants and products are no longer changing.
Answer: B
28) According to the following equilibrium,
2 HI (g) H2 (g) + I2 (g) H = -26.48 kJ/mol the concentration of HI in equilibrium with H2 and I2 will decrease
A) by increasing the pressure of the system.
B) by adding some hydrogen gas.
C) by addition of a catalyst to the reaction.
D) by heating the system.
E) by removing some iodine gas.
Answer: E
29) Which is not usually a factor in determining the rate of a reaction according to collision theory?
A) kinetic energy of the molecules that collide B) orientation of the molecules that collide C) the stability of the product
D) the temperature of the reaction mixture
E) the number of particles per unit volume in the sample Answer: C
30) The equilibrium system PCl5 (g) PCl3 (g) + Cl2 (g) is disturbed by adding chlorine. When equilibrium is reestablished, what can be predicted about the new concentration compared to the original equilibrium concentration?
A) PCl5 is larger, PCl3 larger, Cl2 smaller B) PCl5 is larger, PCl3 larger, Cl2 larger C) PCl5 is larger, PCl3 smaller, Cl2 smaller D) PCl5 is smaller, PCl3 larger, Cl2 larger
E) PCl5 is larger, PCl3 smaller, Cl2 larger Answer: E
31) Determine the value of Kc for the following reaction given the Kp.
CO (g) + Cl2 (g) COCl2 (g) Kp = 15.0 at 300°C (R = 0.0821 L·atm/molK)
A) 706 B) 1.42 × 10-3 C) 369 D) 3.14 E) 0.319
Answer: A
32) For the system CaO (s) + CO2 (g) CaCO3 (s), the equilibrium constant expression is A) CO2
B) 1/ CaO CO2
C) CaCO3 / CaO CO2 D) 1/ CO2
E) CaO [CO2] / CaCO3 Answer: D
33) Consider the reaction below:
CO (g) + H2O (g) CO2 (g) + H2 (g) H° = -41 kJ
All of the following changes would shift the equilibrium to the right except one. Which one would not cause the equilibrium to shift to the right?
A) Decrease the temperature.
B) Add some CO.
C) Increase the partial pressure of H2O.
D) Decrease the container volume.
E) Remove some CO2.
Answer: D
34) At a certain temperature, the equilibrium mixture of the reaction PCl5(g) PCl3 (g) + Cl2 (g) has PPCl5 = 1.5 atm, PPCl3 = 0.10 atm, and PCl2 = 7.50 atm. Calculate the value of Kp at this temperature.
A) 2.0 B) 0.77 C) 1.0 D) 0.50 E) 1.3
Answer: D
35) Which direction will the following reaction (in a 5.0 L flask) proceed if the pressure of CO2(g) is 1.0 atm?
CaCO3 (s) CaO (s) + CO2 (g) Kp = 1.9 × 10-23 A) to the right because Q < Kp
B) to the left because Q < Kp C) to the right because Q > Kp D) to the left because Q > Kp
E) The reaction is at equilibrium.
Answer: D
36) For first-order reactions, the rate constant, k, has the units A) time-1.
B) time mol L-1.
C) time.
D) L mol-1.
E) mol L-1 time-1.
Answer: A
37) Suppose that at some point in a reaction, [A] = 0.50 M and after 290 s, [A] = 0.10 M. What is the average rate of this reaction?
A) 0.000345 M/s B) 0.00138 M/s C) -0.00138 M/s D) 0.400 M/s
E) 116 M/s Answer: B
38) The reaction: 2 NO (g) + Cl2 (g) 2 NOCl (g) is allowed to reach equilibrium. Analysis of the equilibrium mixture shows [NO] = 0.0574, [Cl2] = 0.126, and [NOCl] = 0.248. Calculate Kc for this reaction at this
temperature.
A) 1.00 B) 6.75 × 10-3 C) 2.92 × 10-3 D) 148 E) 34.2
Answer: D
39) The value of Kc is changed when
A) the pressure of the system is changed.
B) the concentration of reactants are changed.
C) the volume of the system is changed.
D) the temperature of the system is changed.
E) a catalyst is added.
Answer: D
40) Which direction will the following reaction (in a 5.0 L flask) proceed if a catalyst is added to the system?
CaCO3 (s) CaO (s) + CO2 (g) Kp = 1.9 × 10-23 A) to the right
B) to the left
C) The equilibrium position will not change but the concentrations of everything will increase.
D) The equilibrium position will not change but the rate will increase.
E) It is impossible to tell without more information.
Answer: D
41) The decomposition of H2O2 is first order with a rate constant k = 3.66 × 10-3 sec-1. If the initial concentration of H2O2 is 405 M, how long will it take, in minutes, for the concentration to drop to 134 M?
A) 0.00405 B) -302 C) 5.03 D) 2.19 E) 302
Answer: C
42) In the reaction: 2A B, [A]/ t = -0.50 M/s. What is the rate of formation of B?
A) 0.25 M/s B) -1.0 M/s C) -0.50 M/s D) -0.17 M/s E) -0.25 M/s
Answer: A
43) Which statement is incorrect?
A) The half-life of a second order reaction is inversely proportional to the initial concentration.
B) The shorter the half-life, the faster is the reaction.
C) The half-life of a first order reaction is directly proportional to the initial concentration.
D) The half-life of a first order reaction is independent of the initial concentration.
E) The half-life of a zero order reaction is directly proportional to the initial concentration (i.e., the greater the concentration the longer the half-life).
Answer: C
44) If the equilibrium concentrations of Cl2 and COCl2 are the same at 395°C, find the equilibrium concentration of CO in the reaction
CO(g) + Cl2 (g) COCl2(g) Kc = 1.2 × 103 at 395°C
A) 4.0×10-4 B) 1.0×10-6 C) 8.3×10-4 D) 1.0×10-8
Answer: C
45) Which statement is not correct regarding the function of a catalyst?
A) It changes the mechanism of a reaction.
B) It lowers the energy of the product causing the reaction to be more exothermic.
C) It lowers the activation energy.
D) It affects the rate of a chemical reaction.
E) None of the above are incorrect.
Answer: B
46) At equilibrium, the value of the reaction quotient, Kp, is 0.636. What will be the value of Qp if the total volume of the reaction shown below is halfed?
A (g) 4 B (g)
A) 0.404 B) 1.27 C) 12.6 D) 5.09 E) 10.2
Answer: D
47) A chemical system is at equilibrium
A) when the rate of the forward reaction becomes zero.
B) when the concentration of reactants and products are equal.
C) when all of the reactants have been used up.
D) when the rates of the forward reaction and the reverse reaction are equal.
E) when the rates of the forward reaction and the reverse reaction are both zero.
Answer: D
48) Initial rate data were obtained for the following reaction:
2 A (g) + 3 B (g) 2 C (g) Experiment Initial
[A], Mol/L Initial
[B], Mol/L Initial Rate
1 0.10 0.10 1.4 × 102
2 0.20 0.10 2.8 × 102
3 0.20 0.20 5.6 × 102
What is the rate law for the reaction?
A) rate = k [A] 2[B]
B) rate = k [A][B]
C) rate = k [A] 2[B] 2 D) rate = k [A]
E) rate = k [A][B] 2 Answer: B
49) Which of the following is not a possible initial rate law for the following reaction?
2 H2 + C2H2 C2H6 A) Rate = k [H2] [C2H2]
B) Rate = k [H2]2 [C2H2]
C) Rate = k [H2]2
D) All of the above rate laws are possible.
E) None of the above rate laws are possible.
Answer: D
50) Consider the hypothetical reaction A + 2B 3C + 2D
Suppose that at one point in the reaction, [A] = 0.46 M, and 100 s later [A] = 0.42 M. During this time period, what is the average (a) rate of reaction in M s-1 and (b) rate of formation of D, expressed in M min-1.
A) 4.0×10-4,4.8×10-6 B) 4.0×10-6,4.8×10-8 C) 2.0×10-4, 4.8×10-4 D) 4.0×10-4, 4.8×10-2 Answer: D
