exam_answers_152C_exam_01_version_b_key

exam_answers_152C_exam_01_version_b_key - - C KEY Ca“ /5...

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Unformatted text preview: - C KEY Ca“ /5 ‘2 ( Viki/003 CHEMISTRY 1 2C HOUR EXAM I (Version b) ___._.__. ~ Winter 2008 Wednesday, January 30, 2008 Name: TA Section: Student Number: TA Name: Score 1 2 GOOD LUCK! Watch sig figs and units. 3 - 4 5 Total (x/100) I. CONCEPTS AND SHORT ANSWER: Answer all questions (subtotal = 52 pts) #5, (U 1. (a) @F) For an ideal, monatomic gases, Cp = Cv + R {3) (b), Why is Cp > (5/2)R for all real, polyatomic gases ? (“Zia/551444 faééblu: Md“; 9/ /'n(‘m;/>3 ‘éyf’ "C 9 wry? w; 2. (a) Consider an ideal gas at 10 °C in a 1.0 liter bulb connected to an evacuated volume of 4.0 liters by a closed valve. Now open the valve, letting the gas expand adiabatically into the larger volume. For this expansion, give the sign (+ or — or O) of each of the following: q w AE AH AS (g) 0 0 0 0 4’ (b) Give a formula for the change in entropy A8 for this expansion {2) AS: (6) 3. indicate which of the following statements is true (T) orfalse (F): (a) _E_ For an ideal gas, E and H can only change if the volume changes. (b) iln a reversible cyclical process, the system returns to its original state, but the universe does not. (c) __F_‘ All spontaneous processes increase the disorder of the surroundings (d) _E_ At constant volume, the enthalpy change is the heat flow in or out of the - system (e) L The maximum work possible in the expansion of an ideal gas corresponds to the irreversible expansion. (f) __7_'_ Thermodynamics concerns changes in state, but not rates of change. Chemistry 152C Page 2 42; 5/) 4. For each of the following forms oxatter, give the standard thermodynamic state(°): (a) pressure of a gas / =1 (b) temperature 293K _ , . (0) pure solids, or liquids flu" "fly/I A94’J (d) solution concentration //I¢ (3) 5. Consider the following sequence of reactions: AH1 2A+SB ——>4C+2D AHz E+B —>C AH3 2F+B —>2D In terms of the enthalpy changes of the individual reactions (AH1, etc), write an expression for the enthalpy change Aern for the following net reaction: 2E + F a A (Z) 6. (a) Calculate the boiling temperature T (in K) of liquid bromine Brz at P=1 atm Brz (i) _> Br2 (9) For this phase transition, the vaporization enthalpy of Bl’z is AH° = 27.5 kJ/mole, and the entropy change is AS° = 83.0 J/(K mole) 7': Ada: 29.5'X/fl?T/wl' As” gsoT/w/e/z (b) At the boiling point, what is the value of: ASuniver, ASsurr ASS),s (a) o ‘83;ij +6?sz 7. Calculate the work (w) done when an ideal gas expands from an initial volume of 3.0 / ) liters to a final volume of 7.0 liters against a constant external pressure of 2 atms. 3 8. In Boltzman’s formula for entropy S= kBIn(Q) , what does 0 represent? {3} @umer 4/ %)2fl5’é‘4¢5 4/9 :jJ—A— Version A@ to -: "75/ A V: —{29A.)(7. 0~:’fl(f) :Lw Chemistry 152C fix 6,) 9. ,For each of the following, give the sign of AS: Page 3 a. _—_ condensing a gas directly to a solid b. _:_ freezing a liquid to a solid 0. i dissolving salt in water to make a solution d. i heating an ideal gas at constant pressure (2) 10. (a) Name two important greenhouse gases increasing due to human activity: ('02 C 2%, N2 0, CFC For the following, circle the most appropriate answer: (C) (b) The natural greenhouse effect warms the Earth about ( 0.3, 3,615) 100) °C (0) The warming over the past century has been approximately (0.0, 0.3, @24) °C (0) Increasing atmospheric C02 is predicted to cause additional warming in this century of about (0.3,@ 10, 30) °c (d) The most abundant fossil fuel is petroleum, natural gas) (e) Complete melting of the Greenland lce Cap would raise global sea—level by (1 2 4 10) meters (f) Currently the global atmospheric C02 concentration is increasing at (0.1, 0.5, 1. 5.0) ppm/yr (parts-per—million) and may be double the natural level by 2050. 11. State the three laws of thermodynamics: /Z) IstLaw: EMU) 6/, éh’i/Pyyf fs C’éuréfl7l (z; 2“dLaw {Fwy} Va. gag-adrr/‘S/ % gmwrse (2) 3rd Law f” fig? 5’ a//rr/4c/Cr§svg 0% €éfc/JC kra 74779 /&‘/a) ,5 gfl’é, ya . Version Chemistry 152C Page 4 #3 n. QUANTITATIVE: Do all four(4) ofthe following (subtotal=48 pts) 0;) 1. The heat capacity at constant pressure of N20 is Cp (N20) = 36.60 J/K mole. If 92.0 grams of N20 is cooled from 185 °C to 45 °C at a constant pressure of 3.00 atm, calculate q, w, AE and AH for this process. {/z)2. A 43.2 gram sample of copper is heated to 98.3 0C and then placed in a calorimeter containing 65.0 9 water at 20.1 0C. The final temperature of the water and copper is 25.3 0C. Calculate the specific heat capacity of the copper (units of J/(g OC)) assuming that all heat lost by the copper is gained by the water. Specific heat capacity of water is 4.18 J/(g 0C) Version A Chemistry 152C Page 5 (/2) 3. Consider a rigid, insulated box with two compartments. One compartment contains 0.300 mol of He(g) at 25.0 0C and 1.00 atm. The other compartment contains 0.700 moi of N2(g) at 95.0 0C and 3.00 atm. Heat can flow between the compartments. What is the final temperature in the box at thermal equilibrium? The molar heat capacities are: Cv = 12.5 J/(K mol) for He Cv = 20.7 J/(Kmol) for N2 (’23.. Calculate AS" for the reduction of aluminum oxide by hydrogen gas: A|203 (s) + 3 H2 (9) --—--> 2 AI (3) + 3 H20 (9) 8° (J/K mol) Al203 48 H2 137 Al 26 H20 194 Version A ...
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This note was uploaded on 04/07/2008 for the course CHEM 152 taught by Professor Chiu during the Spring '08 term at University of Washington.

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exam_answers_152C_exam_01_version_b_key - - C KEY Ca“ /5...

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