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Unformatted text preview: Version 150 Final sutcliffe (51060) 1 This printout should have 41 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points At 600 C, the equilibrium constant for the reaction 2 HgO(s) 2 Hg( ) + O 2 (g) is 2.8. Calculate the equilibrium constant for the reaction 1 2 O 2 (g) + Hg( ) HgO(s) . 1. 0.36 2. 1 . 7 3. 0.60 correct 4. 1.1 5. 1.7 Explanation: 002 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, H is 56 . 8 kJ mol 1 . 1. 0.188 correct 2. 1 . 11 10 4 3. 1 . 32 10 6 4. 15.5 5. 1 . 54 10 7 Explanation: 003 10.0 points Estimate the enthalpy of vaporization of CCl 4 given that at 25 C and 58 C its vapor pressure is 107 and 405 torr, respectively. Assume that the enthalpy of vaporization is independent of the temperature. 1. 486 J mol 1 2. 3.98 kJ mol 1 3. 142 kJ mol 1 4. 48.6 kJ mol 1 5. 33.1 kJ mol 1 correct Explanation: T 1 = 25 C + 273 . 15 = 298 . 15 K P 1 = 107 torr T 2 = 58 C + 273 . 15 = 331 . 15 K P 2 = 405 torr Using the ClausiusClapeyron equation, ln parenleftbigg P 2 P 1 parenrightbigg = H vap R parenleftbigg 1 T 1 1 T 2 parenrightbigg H vap = R ln parenleftbigg P 2 P 1 parenrightbigg 1 T 1 + 1 T 2 = 8 . 314 J mol 1 K 1 298 . 15 K 1 331 . 15 K ln parenleftbigg 405 torr 107 torr parenrightbigg = 33109 . 5 J mol 1 004 10.0 points Consider the solutions I) 0.5 M Na 2 SO 4 , II) 0.6 M NaCl, and III) 1.0 M sugar. What answer gives the expected order of in creasing (lowest, next, highest) osmotic pres sure? 1. I, II, and III 2. III, II, and I correct 3. II, III, and I Version 150 Final sutcliffe (51060) 2 4. II, I, and III 5. III, I, and II Explanation: The equation for osmotic pressure is = M RT where is the osmotic pressure, M is the molarity, and R and T are the same for the ideal gas law. If molarity increases then the osmotic pressure increases (they are directly proportional). Since this is a colligi tive property, it s the number of moles of the particles that is important. The sugar has the largest molarity, but since it does not ion ize, there is only one mole of particles present. Each NaCl ionizes to give two ions so the ef fective molarity is 2(0 . 6) = 1 . 2 M. And lastly Na 2 SO 4 ; this also ionizes and gives three ions, so its effective molarity is 3(0 . 5) = 1 . 5 M. 005 10.0 points Calculate the reduction potential for the Zn 2+  Zn electrode if the Zn 2+ concentra tion is 5 10 3 M. The standard potential for Zn 2+ + 2 e Zn is . 7628 V....
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 Fall '10
 McCord
 Chemistry, Enthalpy, Vaporization

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