# HW12answers - Cheung Anthony – Homework 12 – Due Dec 3...

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Unformatted text preview: Cheung, Anthony – Homework 12 – Due: Dec 3 2006, midnight – Inst: McCord 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Entropy is a state function. 1. False 2. True correct Explanation: 002 (part 1 of 1) 10 points For the four chemical reactions I) 3O 2 (g) → 2O 3 (g) II) 2H 2 O(g) → 2H 2 (g) + O 2 (g) III) H 2 O(g) → H 2 O( ‘ ) IV) 2H 2 O( ‘ ) + O 2 (g) → 2H 2 O 2 ( ‘ ) which ones are likely to exhibit a positive Δ S ? 1. I, III and IV only 2. III and IV only 3. II only correct 4. I and II only 5. All have a positive Δ S . Explanation: The Third Law of Thermodynamics states that the entropy of a perfect pure crystal at 0 K is 0. As disorder, randomness, and de- grees of freedom increase, so does S . Entropy can increase by changing phase from solid to liquid to gas, and by increasing temperature, volume, or number of particles. In reaction I, the final state has less gas par- ticles (and thus less entropy) than the initial state. Therefore Δ S is negative. In reaction II, the final state has more gas particles (and thus more entropy) than the initial state. Therefore Δ S is positive. III describes a phase change. Gases have more degrees of freedom, randomness, and disorder (entropy) than liquids. The final state is a liquid and the initial state is a gas. Therefore Δ S is negative. In reaction IV, the final state has 0 gas particles and the initial state has 1 mole of gas particles. Therefore Δ S is negative. 003 (part 1 of 1) 10 points Place the following in order of increasing en- tropy. 1. solid, gas, and liqiud 2. gas, liqiud, and solid 3. gas, solid, and liqiud 4. solid, liquid, and gas correct 5. liqiud, solid, and gas Explanation: Entropy ( S ) is high for systems with high degrees of freedom, disorder or randomness and low for systems with low degrees of free- dom, disorder or randomness. S (g) > S ( ‘ ) > S (s) . 004 (part 1 of 1) 10 points For the evaporation of water from an open pan at 25 ◦ C, the values of Δ S for the water, the surroundings, and the universe must be, respectively, 1. positive, negative, positive. correct 2. positive, positive, positive. 3. None of these is correct. 4. positive, negative, zero. 5. negative, negative, negative. Explanation: The process is spontaneous, which means Δ S universe > 0 according to the Second Law of Thermodynamics. Entropy ( S ) is high for systems with high degrees of freedom, disorder or randomness Cheung, Anthony – Homework 12 – Due: Dec 3 2006, midnight – Inst: McCord 2 and low for systems with low degrees of free- dom, disorder or randomness....
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HW12answers - Cheung Anthony – Homework 12 – Due Dec 3...

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