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exam_answers_ex_1_vers_B - ’85“ CHEMISTRY 152A HOUR...

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Unformatted text preview: ’85“? CHEMISTRY 152A HOUR EXAM I (Version B) , Fall '04 :Thursday, October 28, 2004 Name: TA Section: __ Student Number: __ *___ TA Name: Score (page) 1 __ (’%l) _ . 2 _'_____ (x GOOD LUCK! I 3 ‘____ (xx/2;: , . 4 ____ (V29) A, SHOW YOUR WORK IN THE SPACE PROVIDED 5 - ' ' (,y/u) (possible points = 100 pts) , Total _____r M”) I. CONCEPTS SHORT ANSWER: . (75 pts) 1. Indicate which of the following quantities a» state function: of” @[email protected]@@@@w .2. In the formula w = — PAY, ’ why the minus (—) sign? Pvt/37 / 5.75.46 ’ . (‘0 ’ calf» PW‘IHJI'QA [AV>0) “79:325/ pox? ~ 3” Fora liquid, AS(vaporization) is (smaller, 1 than AS(fusion). Why? {4) ' U°/’4”" 0"”)? ‘90”. V9faf/ 090/8 ,3- /qr;or fldk p l/b/anc cAO, e «name/qu s-u»' , 5,577 jlwmflr _wr' 131058057)? Via/Gaff. ' ’4. (‘0 For any spontaneous process, which of these terms is always positive? AS(surroundings) AS(SYSt€lYIi) ‘5. Which of the following statements is tr_ue(T) or false (F): (a) (a) All real processes are irreversible 7" (b) In anirreversible cyclical process, the system returns to its original state, but the universe does not. F (c) All spontaneous processes increase the'disorder of the system . ' 6. In the isothermal, irreversible expansion of a gas, give the sign. (9) ( “+” or “—“ or “0” ) of each of the following quantities: w , q AE AH AS AS(surr) AG <0 >0 a 0 >0 4 o <0 (5) pressure P of 1.0 atm. What is w (in Liter—atm)? = - PAV=- ([96,){3J—xa) = _ zrlfl-r 974... 7.‘ A gas expands isothermally from 1.0 to 3.5 liters against a constant external 8. Which of the following properties are extensive? (5*) ~ - . . . temperature concentration . 9. If 50 mL of water at 280K is mixed with 30 mL of water at 330K, what is the final {g} temperature of the mixture? . ééZQ/zaa) + g;J/;;0) I : 299/5 I 10. Consider the follOwing reaction sequence: (a) ' ' , (a) A —+ 2B (b) B —> C +_D (c) E —> 2D In terms of the enthalpies of reaction H(a), etc, write an expression for the enthalpy of reaction for the reaction ‘ ' I ‘A —$-2C+E I ~ ‘ Mm.- A/g, Qua—mg. I? 9% /Z£/~> 2052f. a v» 2C7‘E ' - 11. If a diatomic molecule spontaneously dissociates intoconstituent atoms M 32(g) —> 2B(g) g (a) Predict the signs of AHO‘ A80 and AG0 )0, >0 <0 (b) Would this reaction become non-spontaneous at higher or lower temperature, and why.7 7Z /0W(/ - - J - 7700:45- q ‘ W2$W€Z;W( 41‘1"; (n 74w //)/c; )leixm dm/nmér over Fwd/,2: 7.4,,“ '. 12. For the melting of a Solid X'(s) —> X(l), the enthalpy of fusion AHo = 8.7 k17mol and {5) the entropy of fusion A30 % 46.2 J/ (K mol). Calculate the melting point ( in oC) fig°=0 = 45/174)? v 7-: 4491" . Ar" _. V3 . " . 3 Mn. 0 y_ ' /88/( /38 ‘ 293 Z ~8§C 13. For the same initial conditions (n,P,V) and. final pressure, the adiabatic expansion (LI) of an ideal gas results in 'a (larger l final volume than does that of' an" isothermal expansion. (Indicate . ' ' ct answer) 14. A chemical reaction is determined to have AG0>> 0.- Indicate whether the following _( V/ statements are true(T) or false(P).: ’ . - F (a) the'reaction proceeds very rapidly to the right —> as written. F (b) K(eq)'= 1.0 F (c) K(eq) >> 1.0 F (d) At, final equilibrium, the product concentrations will be much greater ' than the reactant concentrations. - Ion/57' 15. For the chemical reaction A —+»B, give the conditions for spontaneity as a function of - (4) temperature for each of the following cases: ' , _ ' , ' 0: “AMA (a) AS<O . and ‘AH >0 mo} fpfléh (okl‘ qu”; séerVn"! (b) ‘AS<O and AH <0 _ ypmr-{aheoar 97L /0‘V 4’7"”4“ . (C) AS>O hand AH>0 Spawéhlraa; q/ 4/;4 réymzé: (d) 'AS>O and AH<O {fonr‘m'eaur 4* a” *(wpc'w N‘! an ML <7 tea/z in. QUANTITATIVE: Do either one. of the following ' (25 pts) . / QMV‘Céjflo/M'S‘ 16. Consider the reaction: 2 POCl3(g)- —> 2PC13(g) 02 (g) (a) Determine ’AGO (kJ/mol) for this reaction at standard conditions, using AGf 0»(POC13) = 490 kJ/mol . AGf 0 (P03) = —280 kJ/mol i 0 . _' ' (b) If A5 for this reaction is 191 J/K, calculate the temperature at which the reaction just. becomes spontaneous. ’ ' ' 17. Stratospheric ozone (O3) is‘destroyed in the following reaction: . l ‘ / fl ' A - (25) , ‘ ' r m; a». may . wk . l - N0(g) +O3(g) -+ N02(g)+ 02(g) (/9 G #M/W/a (0) Calculate AGf O and K(eq) for this' reaction, givefi the following: AGfO (N02) '= 50 kI/mol AGfO (03) —_~ 171 kJ/m61 ' ’ AGf‘? (N0) =- 93 kJ/mol ...
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