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CH_301-Sutcliffe-HW10

# CH_301-Sutcliffe-HW10 - romasko(qrr58 – Homework 10 –...

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Unformatted text preview: romasko (qrr58) – Homework 10 – sutcliffe – (50985) 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 73 . 0 mmol of a perfect gas at 310 K, the volume of the gas is reduced to 11 . 0% of its initial value. Calculate w for this process. Correct answer: 415 . 29 J. Explanation: w =- nRT ln parenleftbigg V f V i parenrightbigg =- (0 . 073 mol) [8 . 314 J / (mol · K)] × (310 K) ln parenleftbigg 11 100 parenrightbigg = 415 . 29 J 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 second law correct 2. the fourth law 3. the first law 4. the third law 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. It is not a spontaneous chemical reaction; it is driven by an external agency – light. correct 2. This reaction is characterized by an en- ergy change so close to zero that it is essen- tially reversible. 3. Thermodynamics does not apply to living systems. 4. Thermodynamics deals only with closed systems; photosynthesis is an open system. 5. Thermodynamics does not apply to pho- tochemical reactions. 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. 27 . 3 kJ/K 2. 4 . 53 × 10 − 20 J/K 3. 34 . 0 J/K correct 4. 5 . 65 × 10 − 23 J/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) romasko (qrr58) – Homework 10 – sutcliffe – (50985) 2 = 34 . 0425 J / K 005 10.0 points What is the change in entropy of the sys- tem for melting 3 . 5 mol of NH 3 (s) at its nor- mal melting point? T f Δ H ◦ fus T b Δ H ◦ vap (K) (kJ/mol) (K) (kJ/mol) 195 . 4 5 . 65 239 . 7 23 . 4 Correct answer: 101 . 203 J / K....
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CH_301-Sutcliffe-HW10 - romasko(qrr58 – Homework 10 –...

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