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NAU CHM 152 - Practice Exam 2: Chemistry
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Practice Exam 2A CHM 152, General Chemistry II 1. Which of the following statements correctly describes a reaction for which a plot of ln[A] versus time produces a straight line? [a] the rate constant for the reaction can be obtained from the value of the intercept on the y-axis. [b] the rate of the reaction does not depend on the concentration of A. [c] the rate constant is equal to the negative of the slope of the line. [d] the initial concentration of A can be calculated from the intercept on the x-axis. [e] none of the above statements is true. 2. For the reaction, X + Y → Z, the reaction rate is found to depend only upon the concentration of X. A plot of 1/[X] versus time gives a straight line. What is the rate law for this reaction? [a] rate = k[X] [b] rate = k[Y] [c] rate = k[X][Y] [d] rate = k[X]2[Y] [e] rate = k[X]2 3. At 25°C, the rate constant for the first-order decomposition of a pesticide solution is 6.40 × 10−3 min−1. If the starting concentration of the pesticide is 0.0314 M, what concentration will remain after 62.0 minutes at 25°C? [a] 0.0211 M [b] 0.0268 M [c] 0.0310 M [d] 0.0467 M [e] 3.86 M 4. For the 2nd order reaction, A → products, the concentration of A after 444 seconds is 0.598 M. If the rate constant for the reaction is 7.4 × 10−4 M−1s−1, what is the initial concentration of A? [a] 0.598 M [b] 0.831 M [c] 1.67 M [d] 0.744 M [e] 1.34 M 5. At 25°C, the second-order reaction NOCl (g) → NO (g) + ½ Cl2 (g) has a half-life, t1/2, of 5.82 hours when the initial concentration of NOCl is 4.46 M. Starting with a concentration of 4.46 M, how long (in hours) will it take for the reaction to be 75% complete? [a] 1.94 hr [b] 11.6 hr [c] 15.5 hr [d] 17.5 hr [e] 23.0 hr 6. Which one of the following choices is the correct equilibrium constant expression for the reaction below? Fe2O3 (s) + 3 H2 (g) ⇌ 2 Fe (s) + 3 H2O (g) [a] 32 3 2c2 32[Fe O ][H ][Fe] [H O]=K [b] 32c32[H ][H O]=K [c] 2c2 3 2[Fe][H O][Fe O ][H ]=K [d] 2 32c32 3 2[Fe] [H O][Fe O ][H ]=K [e] 32c32[H O][H ]=K 7. At equilibrium, ___________________________ . [a] all chemical processes have ceased. [b] the rate of the forward reaction equals the rate of the reverse reaction. [c] the equilibrium constant for the forward reaction equals the equilibrium constant of the reverse reaction. [d] both (b) and (c) are correct. [e] none of the above is correct.(2) 8. An aqueous equilibrium mixture of CoCl42−, CoBr42−, Cl−, and Br− is present in a flask at 25°C. Which action below will change the value of the equilibrium constant, K, from that which currently describes the concentration relationships of the four species above? [a] Remove some Cl− from the solution. [b] Remove some Br− from the solution. [c] Add more CoCl42− to the solution. [d] Add more CoBr42− to the solution. [e] Put the flask into an 80°C water bath. 9. The reaction, A + B ⇌ X + Y has Kc = 997 at 472 K. At equilibrium, ________________________ . [a] products predominate. [b] reactants predominate. [c] only products exist. [d] only reactants exist. [e] roughly equal molar amounts of products and reactants are present. 10. For the following reactions occurring at 500 K, arrange them in order of increasing tendency to go to completion (least → greatest tendency). 1) 2 NOCl ⇌ 2 NO + Cl2 Kp = 1.7 × 10−2 2) 2 SO3 ⇌ 2 SO2 + O2 Kp = 1.3 × 10−5 3) 2 NO2 ⇌ 2 NO + O2 Kp = 5.9 × 10−5 [a] 1 < 2 < 3 [b] 1 < 3 < 2 [c] 2 < 3 < 1 [d] 3 < 2 < 1 [e] 3 < 1 < 2 11. The equilibrium constant for reaction (1) is K. What is the equilibrium constant for reaction (2)? (1) SO2 (g) + ½ O2 (g) ⇌ SO3 (g) (2) 2 SO3 (g) ⇌ 2 SO2 (g) + O2 (g) [a] K2 [b] 1K [c] 12K [d] 21K [e] −K2 12. At a certain temperature, a 2.00 L flask at equilibrium contains 0.0228 mol HCl, 0.1862 mol Cl2, and 0.0308 mol H2. What is the value of Kc for the equilibrium, 2 HCl (g) ⇌ H2 (g) + Cl2 (g) [a] 0.0909 [b] 11.0 [c] 1.63 × 10−5 [d] 0.252 [e] 0.126(3) 13. Consider the gaseous equilibrium: 2 A ⇌ 2 B + C. Determine the value of the missing “B” concentration at equilibrium in the table below. Assume that all trials of the experiment are conducted at the same temperature. Experiment # [A] at equilibrium [B] at equilibrium [C] at equilibrium 1 0.10 M 0.10 M 0.20 M 2 0.20 M 0.50 M 0.032 M 3 0.35 M ? 0.15 M [a] 0.16 M [b] 0.35 M [c] 0.40 M [d] 0.045 M [e] 0.20 M 14. At 700 K, the reaction 2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g) has an equilibrium constant, Kc = 4.3 × 106, and the following concentrations are present: [SO2] = 0.0100 M, [SO3] = 10.0 M, and [O2] = 0.0100 M. Is the system at equilibrium? If the mixture is not at equilibrium, in which direction will the system shift to reach equilibrium? [a] Yes. The system is at equilibrium. [b] No. The system will proceed from left to right (reactants to products) to achieve equilibrium. [c] No. The system will proceed from right to left (products to reactant) to achieve equilibrium. [d] There is not enough information given in the problem to determine the equilibrium position. 15. Consider the following reaction: N2 (g) + O2 (g) ⇌ 2 NO (g) Kc = 0.25 You start the reaction with 10.0 moles of NO in a 2.0 L vessel. Set up the ICE table for this problem and then set up to solve for x (the concentration of N2). You should end up with a quadratic equation. The quadratic equation in the form, (ax2 + bx + c = 0) is: [a] 3.75x2 − 40x + 100 = 0 [b] 4.25x2 + 20x − 25 = 0 [c] 0.75x2 − 10x + 25 = 0 [d] 3.75x2 + 2.5x − 6.25 = 0 [e] 3.75x2 − 20x + 25 = 0 16. Consider the reaction shown below. N2O4 (g) ⇌ 2 NO2 (g) Determine the value of the equilibrium constant, Kc, for this reaction is an initial concentration of N2O4(g) of 0.0400 M is reduced to 0.0055 M at equilibrium. There is no NO2(g) present at the start of the reaction. [a] 0.87 [b] 13 [c] 0.22 [d] 0.022 [e] 2.2 × 10−4(4) 17. Consider the following reaction at equilibrium. 2 CO2 (g) ⇌ 2 CO (g) + O2 (g) ∆H = −514 kJ Increasing the temperature will _________________ ? [a] increase the concentration of O2(g) at equilibrium. [b] decrease


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NAU CHM 152 - Practice Exam 2: Chemistry

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