F04_E4A - Chemistry 111 Page 1 out of 8 Exam IV/Fall 2004...

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Chemistry 111 Page 1 out of 8 Exam IV /Fall 2004 Answer Key 1. Fact: The equation below applies to isothermal processes. OS = T q rev Substitution of q reversible = n R T ln (V 2 /V 1 ) yields. OS = n R l n V 1 V 2 bl Since the temperature cancels, this last equation now works even if the temperature changes. True or false ? Circle your answer. (02 pts) 2. Consider an ideal gas subjected to a physical process not involving a phase change. If the process is adiabatic, then q = 0. Therefore, if work is done on the system, the temperature must increase. True or false? Circle your answer. (02 pts) First of all, the first law tells us that: Δ E = q + W = n Cv Δ T. Since q = 0, then… Δ E = W = n Cv Δ T Now, it states that work is done ON the system. This means that the quantity W must be positive. This implies that the change in temperature must also be positive. 3. One mole of Xe gas is heated from 20.00°C to 25.00°C. How much heat would be absorbed by this sample if it was being measured in an isobaric calorimeter? Show work. (06 pts) Isobaric calorimeter measures Δ H. Therefore, OH = n Cp OT Since it is a monoatomic ideal gas, we know that Cp = 5/2 R. Therefore, OH = 1 .0 0 m o l # 2 5 #8 .314J /Kmo l # 5 .00K = 104 J . 4. The standard heat of formation of I 2 gas is a positive number. True or false?
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Chemistry 111 Page 2 out of 8 Exam IV /Fall 2004 Answer Key Therefore it should be endothermic. 5. The absolute entropy for O 2 gas is zero at 25°C and 1 atm because it is an element in its standard state. True or false ? Circle! (02 pts) The entropy of anything is only zero at 0 K. 6. Circle the one from the following that should have the highest absolute entropy. (02 pts) CH 4 (g), CH 3 CH 2 CH 3 (g), H 2 O (l), Fe (s), CH 3 -O-CH 2 CH 3 (g) First of all, it has to be a gas. Second of all, it should be the more complex (bigger) one. 7. Given that the following reaction 2 HBr(g) H 2 (g) + Br 2 (l) has a Δ H° = + 72 kJ, what is the molar heat of formation of hydrogen bromide in kJ/mol? (02 pts) The first thing we notice is that this is the opposite of formation. Secondly, it is for two moles of HBr. Therefore, the reaction must be inverted and then divided by two. The same thing would be true for the Δ H. Therefore, the answer must be… - 36 kJ . For questions 8-10 , choose from the following: 1 . PCl 3 (g) + Cl 2 (g) PCl 5 (g) 2 . CH 4 (g) + CO(g) + 1/2 O 2 (g) 2 C(graphite) + 2 H 2 O(l) 3 . N 2 (g) + 3 H 2 (g) 2 NH 3 (g) 4 . CH 3 -O-CH 3 (l) + 3 O 2 (g) 2 CO 2 (g) + 3 H 2 O(g) 8. Write the number of the reaction(s) in which Δ E° = Δ H°. None of them . (02 pts) Since Δ = Δ + R T Δ n
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This note was uploaded on 02/08/2010 for the course CHEM 111 taught by Professor Kenney during the Spring '08 term at Case Western.

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F04_E4A - Chemistry 111 Page 1 out of 8 Exam IV/Fall 2004...

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