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Homework 10-solutions

# Homework 10-solutions - dewitt(aad777 – Homework 10 –...

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Unformatted text preview: dewitt (aad777) – Homework 10 – sutcliffe – (52380) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This is your LAST Homework!!! 001 10.0 points In the isothermal compression of 68.0 mmol of a perfect gas at 325 K, the volume of the gas is reduced to 19.0% of its initial value. Calculate w for this process. Correct answer: 305 . 1 kJ. Explanation: w =- nRT ln parenleftbigg V f V i parenrightbigg w =- (68 / 1000)8 . 314(325) ln(19 / 100) w = 305 . 1 kJ 002 10.0 points The fact that a heat pump requires energy to move heat from a colder object (the outside of a house) to a hotter object (the inside of the house) is a real life observation of which thermodynamic law? 1. the first law 2. the fourth law 3. the third law 4. the second law correct Explanation: The Second Law of Thermodynamics states that in spontaneous changes the universe tends toward a state of greater disorder. In other words, in spontaneous reactions Δ S Univ > 0. Energy must be used to make the reaction spontaneous. 003 10.0 points The oxidation of sugar to carbon dioxide and water is a spontaneous chemical reac- tion. Since we know that reactions that occur spontaneously in one direction cannot occur spontaneously in the reverse direction, how can we understand photosynthesis? 1. Thermodynamics deals only with closed systems; photosynthesis is an open system. 2. It is not a spontaneous chemical reaction; it is driven by an external agency – light. correct 3. Thermodynamics does not apply to pho- tochemical reactions. 4. Thermodynamics does not apply to living systems. 5. This reaction is characterized by an en- ergy change so close to zero that it is essen- tially reversible. Explanation: It is not a spontaneous chemical reaction; it is driven by an external agency – light. 004 10.0 points Imagine that one carbon in buckminster- fullerene (C 60 ) is replaced by a silicon atom, yielding SiC 59 . This molecule can then orient in 60 different ways. What is the entropy of one mole of SiC 59 at T = 0 K? 1. 4 . 53 × 10 − 20 J/K 2. 5 . 65 × 10 − 23 J/K 3. 34 . 0 J/K correct 4. 27 . 3 kJ/K Explanation: n = 1 mol k = 1 . 38066 × 10 − 23 J / k W = 60 N A = 6 . 02214 × 10 23 mol − 1 S = nk N A ln W = (1 mol)(1 . 38066 × 10 − 23 J / k) × (6 . 02214 × 10 23 mol − 1 ) ln(60) = 34 . 0425 J / K 005 10.0 points dewitt (aad777) – Homework 10 – sutcliffe – (52380) 2 WITHDRAWN 006 10.0 points Calculate the boiling point of a liquid for which Δ H vap = 20 kJ / mol and Δ S vap = 140 J / mol · K. Correct answer: 142 . 857 K. Explanation: Δ H vap = 20 kJ / mol Δ S vap = 140 J / mol · K During phase changes Δ G = 0 . Solve for T when Δ G = 0: Δ G = Δ H- T Δ S = 0 T = Δ H Δ S = 20 kJ / mol . 14 kJ / mol · K = 142 . 857 K 007 10.0 points Consider the following processes. (Treat all gases as ideal.) I) The pressure of one mole of oxygen gas is allowed to double isothermally.is allowed to double isothermally....
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Homework 10-solutions - dewitt(aad777 – Homework 10 –...

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