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exam_answers_Version_B_key - I(£V CHElVIISTRY 152C HOUR...

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Unformatted text preview: * I . /(£V(:) . CHElVIISTRY 152C HOUR EXAM I (Version B) Winter '06 Thursday, January 26, 2006 Name; ' . TA Section: Student Number: - TA Name: E Score (page) 1 GOOD LUCK! CNLIl-D-UJN Total ' (x/lOO) - Useful constants; R = 8.314 J/K mole = 0.0821 liter atm/K mole Na = 6.022 x 1023 molecules/mole WWW I. CONCEPTS AND SHORT ANSWER: (subtotal =40 pts) (4/) 1. For a real, polyatomic gas such as C02, indicate Whether the following are true (T) or false (F): (a) Cp = (5/2)R (b)LCp ~ Cv = R )9) 2. The heat of formation for an element in its standard state is (True/False) (a) zero onlgFPO Kelvin (b) defineQero (b) defined by the Sec Law of Thermodynamics (d) must begeasured l “2.) 3. For a spontaneous’process, which of these terms can be negative? AS(surroundings) AS(universe) 5/126er 4. Which of the follovving statements is true (T) or false (F): @ (a) All real processes are reversible @ (b) In a reversible cyclical process, the system returns to its original state, but the universe does not. ' ® (0) All spontaneous processes increase the disorder of the surroundings ( i) 5. In the isothermal and reversible expansion of an ideal gas, give the Sign of each of the following ( C¢+’3 66—“ (‘07, ) W q AE AH ASsys ASsurr AG /- + 0 0 + "‘ —o {4) '6. A gas expands isothermally from 1.0 to 2.5 liters against a'constant external pressure of 1.0 atm. What is the value of the work W (in L-atm)? - = '5',fo V x ~*//,0-77$n)[2.$'l — mu] (col: ~AS'4975M; {4}") 7. If 30 mL of water at 290K is mixed with 50 mL of water at 320K, What is the final temperature . of the mixture? Boflggo (5’290) 5 575 (3&0 (370—5.) 807; = {30) (270) +@}/?2a>_ 7: 3.44912- 74 80- - 309K Wn/My ‘ (I4) 8. Consider the following reaction sequence: (a) A —>2B (b) B '—>'C+D (c) 2D —>£E' In terms of the enthalpies of reactionAH(a), etc, write an expression for the enthalpy of reaction for the reaction ‘ A —>2C+E Mm, = 44/9 + 2.4/4 + we (W) 9. The melting point of tungsten is 3720 K, and the enthalpy of fusion AHQ is 42.5 kJ/mole. What is the entropy change ASO which occurs for this phase transition from solid to liquid tungsten? ' 21;": 4//°-— 7&5“ :6 A5“: A/f'; Vagxxegféw/e 7 £720! {4150:14717’ %’zi - {44) 10. For the chemical reaction A -—> B, give the conditions for spontaneity~ as a function of temperature ' for each of the following cases: ' (a) AS<0 and AH>0 mew-er ;f%7é»poar 5/1 (.7347 (b)AS<O and AH<0 r/oon’éneou: 97L /ow 42%: (c)AS>O and AH>0 5799102433011!“ 4/ 4854 >417»: (d)AS>Opand AH<O g/mwénwur .971 Q// 4%; I QUANTITATIVE: Do all five (5) of the following (subtotal=60pts)’ 11. The heat capacity at constant pressure of N20 is Cp (N20) = 42.30 J/K mole. If 66.0 grams of N20 is cooled' from 185 0C to 45 0C at a constant pressure of 4.00 atm, calculate q, w, AE and AH for this process. ‘ 12. A piece of copper metal of mass=40.0 g is heated to 90.0 0C, then dropped into a. calorimeter containing 85.0 g of water at 25.0 0C. The final temperature of the water and copper is 29.5 0C. Calculate the specific heat capacity ( in units of J/ g 0C) of the copper. (Assume all heat lost by the copper is gained by the water. Specific heat capacity of water is 4.18 J/g.OC) 13. Given the following data: NH3 (g) —> 1/2 N2 (g) + 3/2 H2 (g) AH = 52 kJ 2H2 (g) + 02 (g) a 2H20‘(g) AH=~457 kJ Calculate AH for the following reaction: 2N2(g) '+ 6H20(g) —> 3 02 (g) + 4NH3(g) 14. One mole of an ideal gas with volume of 1.0 L and a pressure of 4.0 atm is allowed to expand isothermally into an evacuated bulb to give a total, volume of 3.0 L. For this change of state, calculate w, q, AS, and q(rev), 7/21/9 - 15. Consider the reaction: ‘ 0sz (g) + 4F2 (g) -> 2CF4 (g) + H2 (g) for which the standard entropy change ' AS0 = - 335 J/K. Use this Value and the following S0 data to calculate the standard entropy So for CF 4 (g) S°(H2 ) = 125 J/K _ 30(0sz ) = 210 J/K ' 'SO(F2 ) = 205 J/K Recall: ASOrxn = 2 ASo(products) — 2 ASo(reactants ) USEFUL FORMULAE ' F AE=q+w 13:7; w=—PAV PV=nRT H=E+PV _ AH=qp (atconstP) ‘ K=°C+273' AH = H (prod) — H (react) { <KE> =§ RT (ideal gas) Cp = CV + R =% R (ideal gas) AH = nCpAT AB = nCVAT Aern = ZAHE (prod) - ZAHE (react) q = nCAT s = kB In Q wreV = ‘ nRT In = " qrev Wrev ' 1n AS = qreV/T AS = ann(V2/V1) AS = 'n(Cp)1n(T2/T1) at conSt P; ASuniV = ASsys + Assm ASsurr = - AH/T AS = - AHfusio'h/T(m.p) G=H-TS VAG=AH—TAS ‘AG°=AH°—TAS° 0 _ o '. o ’ = max Aern —ZS (prod) — ZS (react) AG Wuseful ...
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This test prep 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_Version_B_key - I(£V CHElVIISTRY 152C HOUR...

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