TA practice quiz 6 - CH301 Fall 2010 Practice Quiz 6 1....

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Unformatted text preview: CH301 Fall 2010 Practice Quiz 6 1. Rank the following molecules in terms of increasing real {experimentally‐observed) positional entropy at 0 K. H2O, H2S, Ar 1. H2O < H2S < Ar 2. Ar < H2S < H2O 3. Ar < H2O < H2S 4. H2S < CO2 < Ar 2. If no vibrational modes are active (internal energy only comes from translation and rotation), which of the following molecules will have the largest molar heat capacity. 1. He 2. N2 3. C2H2 4. CO 5. C2H6 3. Imagine that you have a system consisting of just 3 molecules: HCl, HF, and HBr. Imagine that you have 3 spots on a solid for these molecules to stick to when the system is cooled. What is the maximum theoretical positional entropy of the system at 0 K? Assume each of the molecules can land with two possible orientations. (I am sure you know that ln(2) is about .7 and ln(3) is about 1. 1. 0 J K 1 2. 1.3 10 23 J K 1 3. 2.0 10 23 J K 1 4. 5.2 10 23 J K 1 4. Two different ideal gases, A and B, are initially placed into two pistons under identical conditions (P,V,T,n,etc). Which of the following will be the same for any isothermal (T = 0) compression of the gases? I. w II. q E III. a. I only b. II only c. III only d. I and II only e. II and III only f. I, II, and III g. None of these 5. A system composed of one mole of gas is in thermal equilibrium. The gas is then compressed from 4.0 L to 2.0 L under constant external pressure of 2 atm. The change in internal energy of the system is 10 L atm. What is the change in heat for the system in kJ? Assume 1 L atm = .1 kJ I. 6 kJ II. ‐6 kJ III. 0.6 kJ IV. ‐0.6 kJ 6. Rank the entropies of the following systems in terms of decreasing entropy: I. Pure ethanol (liquid) II. Table salt dissolved in ethanol III. Pure ethanol (solid) IV. A 50/50 mixture of ethanol and methanol 1. II > IV > I > III 2. IV > II > I > III 3. II > IV > III > I 4. III > I > IV > II 5. III > I > II > IV 6. I > III > IV > II 7. II > IV > I > III 7. A process has a Ssurr of 8 J K 1 at 27 C . Estimate the value of Ssurr when the temperature is lowered to 173 C . (Hint: find Hsys first.) Would you have predicted this new Ssurr to be larger or smaller at this colder temperature? 1. 45 J K 1 2. 16 J K 1 3. 24 J K 1 4. 42 J K 1 8. Assume that G for the process in question 7 at 25 oC is ‐165 J. What is Suniv for this process? (Hint: find Ssys first.) 1. 7.5 J/K 2. .5 J/K 3. ‐.5 J/K 4. ‐7.5 J/K ...
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