# hw 8 - shah(rps587 Homework 8 mcdevitt(52365 This print-out...

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shah (rps587) – Homework 8 – mcdevitt – (52365) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points Is an exothermic reaction spontaneous? 1. Sometimes. correct 2. Yes, always. 3. No, never. Explanation: Δ G is negative For spontaneous reactions. Δ G = Δ H - T Δ S Δ H is negative For exothermic reactions. The value oF Δ G is also dependent on T and Δ S , so Δ H is not enough to determine the spon- teneity oF a reaction. 002 10.0 points According to the Second Law oF Thermody- namics, For any spontaneous process 1. The entropy oF the universe will tend toward zero. 2. The entropy oF the system will decrease. 3. Heat will be released into the surround- ings increasing the entropy oF the surround- ings. 4. The entropy oF the system will increase. 5. The total entropy oF the combined system and surroundings will increase. correct Explanation: The Second Law States that For a sponta- neous process the total entropy oF the sys- tem and the surroundings combined (which is Δ S univ ) must increase. 003 10.0 points Rank the Following systems in terms oF in- creasing entropy: a) 1 mol oF pure ice b) 1 mol oF water with 1 mol oF salt dissolved in it. c) 1 mol oF pure water 1. b < a < c 2. a < c < b correct 3. c < a < b 4. b < c < a 5. a < b < c 6. c < b < a Explanation: Entropy increases as systems go through endothermic phase transitions and when there is more matter or more dispersed matter present. 004 10.0 points ±or the process H 2 O(g) H 2 O( ) at 1 atm and 100 C, the change in entropy is 1. positive. 2. negative. correct 3. zero. Explanation: Gases are more disordered than liquids, so Δ S For condensation will be negative. 005 10.0 points Which physical state has the lowest entropy? 1. All have the same entropy. 2. liquid 3. gas 4. solid correct Explanation: Entropy ( S ) is high For systems with high degrees oF Freedom, disorder or randomness

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shah (rps587) – Homework 8 – mcdevitt – (52365) 2 and low for systems with low degrees of free- dom, disorder or randomness. S (g) > S ( ) > S (s) . 006 10.0 points Generally speaking, entropy will increase when 1. temperature is decreased. 2. there is a phase change from liquid to solid. 3. mixtures are separated into pure compo- nents. 4. the volume occupied by a group of molecules decreases. 5. heat is added to a system. correct Explanation: Entropy will INCREASE when volumes in- crease, temperatures increase, and anytime a mixture becomes more disordered. A liquid to solid phase change is a decrease in entropy. Thus the correct choice is that heat is added to the system – which typically results in a temperature increase. 007
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## This note was uploaded on 05/07/2009 for the course CH 52365 taught by Professor Mcdevitt during the Spring '09 term at University of Texas.

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hw 8 - shah(rps587 Homework 8 mcdevitt(52365 This print-out...

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