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Exam1_Solutions - Version 175 Exam 1 Sutclie(52410 This...

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Version 175 – Exam 1 – Sutcliffe – (52410) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The vapor pressure of all liquids 1. is the same at their freezing points. 2. increases with volume of liquid present. 3. increases with temperature. correct 4. is the same at 100 C. 5. decreases with the increasing volume of the container. Explanation: As temperature (kinetic energy) increases, rate of evaporization increases and rate of con- densation decreases; therefore, vapor pressure will increase with increasing temperature. 002 10.0 points Consider the phase diagram for sulfur be- low. 10 5 1300 368 424 Solid Rhombic Solid Monoclinic Liquid Gas Pressure, atm Temperature, K -→ At 424 K and 1300 atm, 1. rhombic sulfur, monoclinic sulfur, sulfur liquid, and sulfur gas exist in equilibrium. 2. rhombic sulfur, monoclinic sulfur, and liquid sulfur exist in equilibrium. correct 3. only rhombic sulfur and sulfur gas exist in equilibrium. 4. only rhombic sulfur is present. 5. only monoclinic sulfur is present. Explanation: (424 K, 1300 atm) is one of the three triple points. 003 10.0 points For the vaporization of water at some temper- ature, which of the following is FALSE? 1. Δ S is positive. 2. The process is endothermic. 3. Δ G will increase with increasing temper- ature. correct 4. Δ G can be negative or positive depending on the pressure. Explanation: At standard phase change points, the pro- cess is in equilibrium. At equilibrium Δ G = 0, but if we change the pressure or temper- ature Δ G can be positive or negative. Va- porization requires energy to be input into the system, so vaporization is endothermic. Gases are more disordered than liquids, so Δ S for vaporization is positive. If we increase the temperature, the liquid will spontaneously go to gas phase. Δ G for spontaneous changes is negative. 004 10.0 points The equilibrium constant K for the dissocia- tion of N 2 O 4 (g) to NO 2 (g) is 1700 at 500 K. Predict its value at 300 K. For this reaction, Δ H is 56 . 8 kJ · mol 1 . 1. 1 . 54 × 10 7 2. 1 . 11 × 10 4 3. 15.5
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Version 175 – Exam 1 – Sutcliffe – (52410) 2 4. 0.188 correct 5. 1 . 32 × 10 6 Explanation: 005 10.0 points Consider the reaction A + B C with Δ G 0 = +120 J. Suppose we start with a mixture of an equal number of moles of A and B. Which of the following is true? 1. Some C will be formed if enough time is allowed for the reaction. 2. The reaction is considered spontaneous. 3. Nothing can be said about the reaction since Δ H and Δ S are not given. 4. No C will be formed since Δ G 0 is +. correct 5. All of A and B will react to form C if enough time is allowed for the reaction. Explanation: A process is nonspontaneous if Δ G is posi- tive. C will not form since Δ G is +. 006 10.0 points For the reaction N 2 O 5 (s) 2 NO 2 (g) + 1 2 O 2 (g) , Δ H r = 109 . 5 kJ · mol 1 at 298 K. At con- stant temperature and pressure, which of the following statements is true?
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