FINALexam_sutcliffe

# FINALexam_sutcliffe - Version 150 – Final – sutcliffe...

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Unformatted text preview: Version 150 – Final – sutcliffe – (51060) 1 This print-out should have 41 questions. Multiple-choice 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( ℓ ) + O 2 (g) is 2.8. Calculate the equilibrium constant for the reaction 1 2 O 2 (g) + Hg( ℓ ) → 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, Δ 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 Clausius-Clapeyron equation, ln parenleftbigg P 2 P 1 parenrightbigg = Δ H ◦ vap R parenleftbigg 1 T 1- 1 T 2 parenrightbigg Δ 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 π = M RT where π 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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FINALexam_sutcliffe - Version 150 – Final – sutcliffe...

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