Practice test Chapter 12 and 13

Practice test Chapter 12 and 13 1. Which of the following pure liquids is the best solvent for carbon disulfide? A) C6H6(l) B) NH3(l) C) CH3OH(l) D) H2O(l) E) HBr(l) 2. How does the solubility of a gas in a solvent depend on pressure and temperature? A) Increasing the partial pressure of the gas while increasing the temperature increases the solubility of the gas. B) Decreasing the partial pressure of the gas while decreasing the temperature increases the solubility of the gas. C) Increasing the partial pressure of the gas while decreasing the temperature increases the solubility of the gas. D) Decreasing the partial pressure of the gas while increasing the temperature increases the solubility of the gas. E) Gas solubility is unaffected by pressure or temperature. 3. A concentrated perchloric acid solution has a density of 1.67 g/ml at 25 C and is 11.7 M. What is the percent by mass of HClO4 in the solution? A) 70.4% HClO4 by mass B) 0.702% HClO4 by mass C) 1.42% HClO4 by mass D) 0.699% HClO4 by mass E) 60.2% HClO4 by mass 4. If 12.7 g of naphthalene, C10H8, is dissolved in 104.6 g of chloroform, CHCl3, what is the molality of the solution? A) 0.0992 m B) 14.5 m C) 0.949 m D) 0.108 m E) 0.113 m 5. What is the molality of a 20.0% by mass hydrochloric acid solution? The density of the solution is 1.0980 g/ml. A) 0.0220 m B) 6.86 m C) 0.200 m D) 5.68 m E) 6.02 m 6. What is the vapor pressure at 20 C of an ideal solution prepared by the addition of 8.87 g of the nonvolatile solute urea, CO(NH2)2, to 57.6 g of methanol, CH3OH? The vapor pressure of pure methanol at 20 C is 89.0 mmhg. A) 6.75 mmhg

B) 69.1 mmhg C) 77.1 mmhg D) 82.2 mmhg E) 19.9 mmhg 7. What is the boiling-point change for a solution containing 0.432 mol of naphthalene (a nonvolatile, nonionizing compound) in 250. g of liquid benzene? (Kb = 2.53 C/m for benzene) A) 4.37 C B) 5.86 C C) 0.273 C D) 1.46 C E) 1.093 C 8. For a dilute solution of (NH4)3PO4, the van t Hoff factor (i) would be approximately A) 4. B) 2. C) 3. D) 1. E) 5. 9. For the hypothetical reaction A + 2B 2C + D, the initial rate of disappearance of A is 2.0 10 2 mol/(l s). What is the initial rate of disappearance of B? A) 8.0 10 2 mol/(l s) B) 4.0 10 2 mol/(l s) C) 1.4 10 1 mol/(l s) D) 4.0 10 4 mol/(l s) E) 1.4 10 2 mol/(l s) 10. Consider the reaction aa + bb dd + ee C = catalyst The rate law is Rate = k[a] q [B] r [C] s Which of the following statements is incorrect? A) The exponents q and r are always equal to the coefficients a and b, respectively. B) The overall reaction order is q + r + s. C) The exponent s must be determined experimentally. D) The symbol k represents the rate constant. E) The exponents q, r, and s are often integers. 11. For a second-order reaction, what are the possible units of the rate constant? A) L 1 s 1 B) mol L 1 s 1 C) s D) L. mol 1 s 1 E) mol L 1

12. The rate law for the chemical reaction 5Br (aq) + BrO3 (aq) + 6H + (aq) 3Br2(aq) + 3H2O(l) has been determined experimentally to be Rate = k[br ][BrO3 ][H + ] 2. What is the overall order of the reaction? A) 3 B) 5 C) 4 D) 2 E) 1 13. For a certain reaction of the general form aa products, the experimental data plotted as 1/[A] versus time is linear. The slope of this plot must equal A) 1. B) the rate constant. C) one over the rate constant. D) the negative of the rate constant. E) 1. 14. Which of the following changes will affect the activation energy of a reaction? 1. Increasing or decreasing the reaction temperature. 2. Adding a catalyst. 3. Increasing or decreasing the reactant concentrations. A) 1 only B) 2 only C) 3 only D) 1 and 2 E) 2 and 3 15. When the concentrations of the reactants are increased, the rate of the reaction increases. This is best explained by A) an increase in the fraction of molecules that have enough energy to react. B) an increase in the rate constant. C) an increase in the average potential energy of the molecules. D) an increase in the frequency of the molecular collisions. E) an increase in the kinetic energy of the molecules. 16. 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 E) 1, 2, and 3 17. Which of the following is not a postulate of collision theory? A) Reactant molecules must collide to react. B) Reactant molecules must collide with a certain minimum energy in order to form products. C) Reactant molecules must collide with the correct orientation in order to form products. D) The rate constant is directly proportional to the energy of activation. E) The maximum in the potential energy curve, the activation energy, is determined by the structure of the activated complex or transition state. 18. For the first-order reaction 1/2 N2O4(g) NO2(g); H = 28.6 kj the activation energy is 53.7 kj/mol. What is the activation energy for the reverse reaction? A) 15.2 kj/mol B) 82.3 kj/mol C) 53.7 kj/mol D) 25.1 kj/mol E) 53.7 kj/mol 19. The acid-catalyzed reaction of acetone, CH3COCH3, with iodine can be represented by the equation CH3COCH3 + I2 CH2ICOCH3 + H + + I It is found experimentally that the reaction is first-order with respect to both acetone and the hydrogen ion. The rate of the reaction is independent of the iodine concentration. Which of the following conclusions could be drawn from the experimental results? 1. The uncatalyzed reaction would have a different pathway. 2. Iodine is involved in the rate-determining step.

3. The reaction takes place stepwise. A) 1 only B) 2 only C) 3 only D) 1 and 3 E) 1, 2, and 3 20. In a chemical reaction at constant temperature, the addition of a catalyst A) provides an alternative reaction pathway with a different 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. E) decreases the energy released in the chemical reaction. 21. Two substances A and B react with each other in such a way that one-half of A remains after 25 min and one-fourth of A remains after 50 min. Doubling the concentration of B while keeping the concentration of A fixed doubles the rate of the reaction. This reaction is A) first-order in both A and B. B) zero-order in both A and B. C) second-order in A and first-order in B. D) first-order in A and second-order in B. E) second-order in both A and B. The following problems are representative of the types of problems you will be asked to solve on part II. 22. What is the molar mass of an aromatic hydrocarbon if 0.85 g of the compound depresses the freezing point of 128 g of benzene by 0.37 C? (Kf for benzene is 5.12 C/m.) 23. A compound containing carbon and nitrogen has a composition of 46.16% carbon and 53.84% nitrogen by mass. A solution prepared by dissolving 1.542 g of this compound in 30.00 g of carbon tetrachloride, CCl4, produces a solution that boils at 81.69 C. What is the molecular formula of the compound? (Kb for CCl4 is 5.03 C/m, and pure CCl4 has a freezing point of 76.72 C.) 24. Calculate the molecular weight of a small protein if a 0.24-g sample dissolved in 108 ml of water has an osmotic pressure of 9.5 mmhg at 22 C. (R = 0.0821 L atm/(k mol)) 25. The nuclide 188 W decays by a first-order process with a rate constant of 1.0 10 2 d 1. How long will it take for 91% of the initial amount of 188 W to be consumed? 26. A first-order chemical reaction is observed to have a rate constant of 25 min 1. What is the corresponding half-life for the reaction? 27. The rate constants for the first-order decomposition of a compound are 6.19 10 4 s 1 at 43 C and 2.71 10 3 s 1 at 65 C. What is the value of the activation energy for this reaction? (R = 8.31 J/(mol K))

28. A suggested mechanism for the decomposition of ozone is as follows: O3 O2 + O fast equilibrium O + O3 2O2 slow step What is the rate law predicted by this mechanism?

Practice test Chapter 12 and 13 Answer Section 1. ANS: A PTS: 1 DIF: easy REF: 12.2 OBJ: Determine when a molecular solution will form when substances are mixed. TOP: solutions solution formation KEY: solubility molecular solution 2. ANS: C PTS: 1 DIF: easy REF: 12.3 OBJ: Explain how the solubility of a gas changes with temperature. TOP: solutions solution formation KEY: effect of temperature and pressure on solubility 3. ANS: A PTS: 1 DIF: easy REF: 12.4 OBJ: Calculate mass percentage of solute. (Example 12.2) TOP: solutions colligative properties 4. ANS: C PTS: 1 DIF: easy REF: 12.4 OBJ: Calculate the molality of solute. (Example 12.3) TOP: solutions colligative properties KEY: expressing concentration molality 5. ANS: B PTS: 1 DIF: moderate REF: 12.4 OBJ: Calculate the molality of solute. (Example 12.3) TOP: solutions colligative properties KEY: expressing concentration conversion of concentration units 6. ANS: D PTS: 1 DIF: easy REF: 12.5 OBJ: Calculate vapor-pressure lowering. (Example 12.9) TOP: solutions colligative properties KEY: vapor pressure of a solution vapor pressure lowering 7. ANS: A PTS: 1 DIF: easy REF: 12.6 OBJ: Calculate boiling-point elevation and freezing-point depression. (Example 12.10) TOP: solutions colligative properties KEY: boiling point elevation 8. ANS: A PTS: 1 DIF: easy REF: 12.8 OBJ: Determine the colligative properties of ionic solutions. (Example 12.14) TOP: solutions colligative properties NOT: REVISED 9. ANS: B PTS: 1 DIF: easy REF: 13.1 OBJ: Explain how the different ways of expressing reaction rates are related. (Example 13.1) KEY: change of concentration with time 10. ANS: A PTS: 1 DIF: easy REF: 13.3 OBJ: Define and provide examples of a rate law, rate constant, and reaction order. KEY: dependence of rate on concentration determining the rate law

11. ANS: D PTS: 1 DIF: easy REF: 13.3 OBJ: Define and provide examples of a rate law, rate constant, and reaction order. 12. ANS: C PTS: 1 DIF: easy REF: 13.3 OBJ: Determine the order of reaction from the rate law. (Example 13.3) KEY: dependence of rate on concentration reaction order 13. ANS: B PTS: 1 DIF: easy REF: 13.4 OBJ: Plot kinetic data to determine the order of a reaction. 14. ANS: B PTS: 1 DIF: easy REF: 13.5 OBJ: Explain activation energy (Ea). 15. ANS: D PTS: 1 DIF: easy REF: 13.5 OBJ: Describe how temperature, activation energy, and molecular orientation influence reaction rates. KEY: collision theory 16. ANS: D PTS: 1 DIF: moderate REF: 13.5 OBJ: Describe and interpret potential-energy curves for endothermic and exothermic reactions. 17. ANS: E PTS: 1 DIF: moderate REF: 13.5 OBJ: Describe and interpret potential-energy curves for endothermic and exothermic reactions. 18. ANS: D PTS: 1 DIF: easy REF: 13.5 OBJ: Describe and interpret potential-energy curves for endothermic and exothermic reactions. KEY: collision theory 19. ANS: D PTS: 1 DIF: moderate REF: 13.8 OBJ: Determine the rate law from a mechanism with an initial slow step. (Example 13.11) TOP: rates of reaction reaction mechanism KEY: the rate law and the mechanism rate determining step 20. ANS: A PTS: 1 DIF: easy REF: 13.9 OBJ: Indicate how a catalyst changes the potential energy curve of a reaction. TOP: rates of reaction reaction mechanism KEY: catalysis 21. ANS: A PTS: 1 DIF: moderate REF: 13.3 OBJ: Determine the rate law from initial rates. (Example 13.4) KEY: dependence of rate on concentration determining the rate law 22. ANS: 93 g/mol 92 PTS: 1 DIF: moderate REF: 12.6 OBJ: Calculate the molecular mass from freezing-point depression. (Example 12.12) TOP: solutions colligative properties KEY: freezing point depression

23. ANS: C2N2 PTS: 1 DIF: difficult REF: 12.6 OBJ: Calculate the molecular mass from freezing-point depression. (Example 12.12) TOP: solutions colligative properties KEY: freezing point depression 24. ANS: 4.3 10 3 g/mol PTS: 1 DIF: moderate REF: 12.7 OBJ: Calculate osmotic pressure. (Example 12.13) TOP: solutions colligative properties KEY: osmotic pressure colligative properties 25. ANS: 240 d PTS: 1 DIF: moderate REF: 13.4 OBJ: Use an integrated rate law. (Example 13.5) KEY: integrated rate laws first-order reaction 26. ANS: 1.7 s PTS: 1 DIF: easy REF: 13.4 OBJ: Relate the half-life of a reaction to the rate constant. (Example 13.6) KEY: integrated rate laws half-life 27. ANS: 59.6 kj/mol PTS: 1 DIF: moderate REF: 13.6 OBJ: Use the Arrhenius equation. (Example 13.7) KEY: Arrhenius equation 28. ANS: Rate = PTS: 1 DIF: moderate REF: 13.8 OBJ: Determine the rate law from a mechanism with an initial fast, equilibrium step. (Example 13.12) TOP: rates of reaction reaction mechanism KEY: the rate law and the mechanism