Answer Key

Quiz 7 Version A Chem 167 October 23, 2008Answer KeyName __________________________Recitation Section Number _____________This is a closed-note, closed-book quiz. You should work individually. You may lose credit for unclear,disorganized, or illegible work. You will be allowed take 15 minutes to complete the quiz.1) (4 pts) Suppose you have two colorless molecular liquids, one boiling at -84 o C, the other at34 o C and both at atmospheric pressure (1 atm). Circle all the statements that are TRUE. (Forwrong answers, points will be taken off)a) The higher-boiling liquid has greater total intermolecular forces than the other.b) The lower-boiling liquid must consist of nonpolar molecules.c) The higher-boiling liquid must have stronger hydrogen bonding.d) Both liquids have identical vapor pressures (760 mmHg) at their normal boiling point.e) At 34 o C both liquids have vapor pressures of 760 mmHg.2) (2 pts) A reaction has an activation energy of 100 kJ and an overall energy change of reactionof 60 kJ. Which diagram best describes this reaction? In each of the following potential energydiagram, the horizontal axis is the reaction coordinate and the vertical axis is potential energyin kJ. (Circle your answer)A) B) C)D) E)

3) (4 pts) Consider the combustion of octane (C 8 H 18 ):C 8 H 18 (l) + 12 O 2 (g) 8CO 2 (g) + 9 H 2 O (g)If oxygen is consumed at the rate of 2.5 atm/h, at what rate CO 2 and H 2 O would be produced?(Report your answer in proper unit and correct number of sig figs)[Hint: write expressions for relative rates]Δ[C H ]Rate = − 8 18 1= −Δt12Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtGiven that −Δ[O 2]= 2.5 atm/hΔtFrom the above rate expression, we know that− 121Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtTherefore,Δ[CO 2]Δt= 128Δ[O 2]Δt= 128 × 2.5 atm/h = 1.7 atm/handΔ[H 2O]Δt= 129Δ[O 2]Δt= 129 × 2.5 atm/h = 1.9 atm/hPlease note that the rate is always expressed as a positive number by convention.

Quiz 7 Version B Chem 167 October 23, 2008Answer KeyName __________________________Recitation Section Number _____________This is a closed-note, closed-book quiz. You should work individually. You may lose credit for unclear,disorganized, or illegible work. You will be allowed take 15 minutes to complete the quiz.1) (4 pts) Suppose you have two colorless molecular liquids, one boiling at -84 o C, the other at34 o C and both at atmospheric pressure (1 atm). Circle all the statements that are TRUE. (Forwrong answers, points will be taken off)a) The lower-boiling liquid must consist of nonpolar molecules.b) The higher-boiling liquid has greater total intermolecular forces than the other.c) Both liquids have identical vapor pressures (760 mmHg) at their normal boiling point.d) The higher-boiling liquid must have stronger hydrogen bonding.e) At 34 o C both liquids have vapor pressures of 760 mmHg.2) (2 pts) A reaction has an activation energy of 40 kJ and an overall energy change of reaction of−100 kJ. Which diagram best describes this reaction? In each of the following potential energydiagram, the horizontal axis is the reaction coordinate and the vertical axis is potential energyin kJ. (Circle your answer)A) B) C)D) E)

3) (4 pts) Consider the combustion of octane (C 8 H 18 ):C 8 H 18 (l) + 12 O 2 (g) 8CO 2 (g) + 9 H 2 O (g)If oxygen is consumed at the rate of 4.5 atm/h, at what rate CO 2 and H 2 O would be produced?(Report your answer in proper unit and correct number of sig figs)[Hint: write expressions for relative rates]Δ[C H ]Rate = − 8 18 1= −Δt12Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtGiven that −Δ[O 2]= 4.5 atm/hΔtFrom the above rate expression, we know that− 121Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtTherefore,Δ[CO 2]Δt= 128Δ[O 2]Δt= 128 × 4.5 atm/h = 3.0 atm/handΔ[H 2O]Δt= 129Δ[O 2]Δt= 129 × 4.5 atm/h = 3.4 atm/hPlease note that the rate is always expressed as a positive number by convention.

Quiz 7 Version C Chem 167 October 23, 2008Answer KeyName __________________________Recitation Section Number _____________This is a closed-note, closed-book quiz. You should work individually. You may lose credit for unclear,disorganized, or illegible work. You will be allowed take 15 minutes to complete the quiz.1) (4 pts) Suppose you have two colorless molecular liquids, one boiling at -84 o C, the other at34 o C and both at atmospheric pressure (1 atm). Circle all the statements that are TRUE. (Forwrong answers, points will be taken off)a) At 34 o C both liquids have vapor pressures of 760 mmHg.b) The lower-boiling liquid must consist of nonpolar molecules.c) The higher-boiling liquid has greater total intermolecular forces than the other.d) Both liquids have identical vapor pressures (760 mmHg) at their normal boiling point.e) The higher-boiling liquid must have stronger hydrogen bonding.2) (2 pts) A reaction has an activation energy of 140 kJ and an overall energy change of reactionof 100 kJ. Which diagram best describes this reaction? In each of the following potentialenergy diagram, the horizontal axis is the reaction coordinate and the vertical axis is potentialenergy in kJ. (Circle your answer)A) B) C)D) E)

3) (4 pts) Consider the combustion of octane (C 8 H 18 ):C 8 H 18 (l) + 12 O 2 (g) 8CO 2 (g) + 9 H 2 O (g)If oxygen is consumed at the rate of 6.5 atm/h, at what rate CO 2 and H 2 O would be produced?(Report your answer in proper unit and correct number of sig figs)[Hint: write expressions for relative rates]Δ[C H ]Rate = − 8 18 1= −Δt12Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtGiven that −Δ[O 2]= 6.5 atm/hΔtFrom the above rate expression, we know that− 121Δ[O 2] 1=Δt8Δ[CO 2]Δt= 91Δ[H 2O]ΔtTherefore,Δ[CO 2]Δt= 128Δ[O 2]Δt= 128 × 6.5 atm/h = 4.3 atm/handΔ[H 2O]Δt= 129Δ[O 2]Δt= 129 × 6.5 atm/h = 4.9 atm/hPlease note that the rate is always expressed as a positive number by convention.