Ch 301 HW 10

Ch 301 HW 10 - – Homework 10 – Sutcliffe –(52380 1...

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Unformatted text preview: – 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 72.0 mmol of a perfect gas at 359 K, the volume of the gas is reduced to 18.0% of its initial value. Calculate w for this process. Correct answer: 368 . 5 kJ. Explanation: w =- nRT ln parenleftbigg V f V i parenrightbigg w =- (72 / 1000)8 . 314(359) ln(18 / 100) w = 368 . 5 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 fourth law 2. the first 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 does not apply to pho- tochemical reactions. 2. This reaction is characterized by an en- ergy change so close to zero that it is essen- tially reversible. 3. It is not a spontaneous chemical reaction; it is driven by an external agency – light. correct 4. Thermodynamics deals only with closed systems; photosynthesis is an open system. 5. Thermodynamics does not apply to living systems. 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. 27 . 3 kJ/K 4. 34 . 0 J/K correct 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 – Homework 10 – Sutcliffe – (52380) 2 005 10.0 points What is the change in entropy of the sys- tem for freezing 4 mol of CH 3 OH( ℓ ) at its normal freezing point? T f Δ H ◦ fus T b Δ H ◦ vap (K) (kJ/mol) (K) (kJ/mol) 175 . 2 3 . 16 337 . 8 35 . 3 Correct answer: 72 . 1461 J / K. Explanation: Δ H fus = 3160 J / mol T = 175 . 2 K n = 4 mol Δ S system = Δ H system T = (4 mol)(3160 J / mol) 175 . 2 K = 72 . 1461 J / K 006 10.0 points Calculate the boiling point of a liquid for which Δ H vap = 33 kJ / mol and Δ S vap = 136 J / mol · K....
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Ch 301 HW 10 - – Homework 10 – Sutcliffe –(52380 1...

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