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hw9 - Killough Ian Homework 9 Due Dec 5 2006 4:00 pm Inst...

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Killough, Ian – Homework 9 – Due: Dec 5 2006, 4:00 pm – Inst: Donna C Lyon 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. This is the final homework assignment for the semester. It is due Tuesday, December 5, by 4:00PM. 001 (part 1 of 1) 10 points For a given transfer of energy, a greater change in disorder occurs when the temperature is high. 1. True 2. False correct Explanation: 002 (part 1 of 1) 10 points When a liquid boils, which of the following statements is true? 1. Δ S < 0 2. Δ T < 0 3. Δ S > 0 correct 4. Δ T > 0 Explanation: Gas phase molecules have more energy and freedom of motion than liquid phase molecules, so gases are more random. Boil- ing causes a system to go from a less random state to a more random state. Δ S is positive when disorder (randomness) increases. T is constant during phase changes. 003 (part 1 of 1) 10 points When a sugar cube dissolves in a cup of coffee (an endothermic process), entropy changes of the sugar plus water, the surroundings, and the universe are, respectively, 1. negative, positive, positive. 2. positive, positive, positive. 3. negative, negative, negative. 4. None of these is correct. 5. positive, negative, positive. correct Explanation: Let’s consider each of the entropy changes individually. Δ S sys : The entropy of any substance in- creases as the substance goes from solid to liquid to gas. Solutions are inherently more disordered than pure substances, so in our system (the process inside the coffee cup) en- tropy increases when we dissolve the sugar cube in water; i.e., Δ S sys is positive. Δ S surr : Here we know that the dissolution process is endothermic. The system draws heat from the surroundings, causing molec- ular motion immediately around the coffee cup to slow down. In turn, as molecules slow down, less random motion occurs, and entropy is decreased, causing Δ S surr to be negative. Δ S univ : The process of dissolving sugar in water is spontaneous, so Δ S univ must be pos- itive by the Second Law of Thermodyamics. (In spontaneous changes, the universe tends toward a state of greater disorder.) 004 (part 1 of 1) 10 points Liquid water freezing to crystalline ice is an example of a system going to a state with a higher degree of order. Which of the following is the best explanation of how this process can be compatible with the Second Law of Thermodynamics? 1. A higher degree of order means an in- crease in entropy, which is exactly what the Second Law requires. 2. Heat is flowing out of the system re- versibly, so it is allowed. 3. Since the process is not occurring at zero Kelvin, the Second Law is not relevant.

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Killough, Ian – Homework 9 – Due: Dec 5 2006, 4:00 pm – Inst: Donna C Lyon 2 4. The surroundings are undergoing changes in the direction of greater disorder. correct 5. Since no chemical change is taking place, the degree of order is not relevent.
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