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# exam_answers_Exam_1_key - CiHEI'H‘IISTRY 152A HOUR EXAM...

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Unformatted text preview: CiHEI'H‘IISTRY 152A HOUR EXAM | {Version B) FALL '06 Thursday, October 26, 2006 Name: TA Section: StudentiNumber: TA Name: I Score 1 2 GOOD liUCKl 3 . 4 - 5 . Total . (xMOO) I. CONCEPTS AND SHORT ANSWER: Answer all questions (subtotal = 48 pts) 1. For a real. polyatomic gases, Cp = Cv + R . _ I _ _ I H ELI/giggle; (mi: 3mm 011%ch a? Mdonqued-ﬁ) l/D'l'a‘ﬁon if Vllomﬁorl, Main Com-rurng UP (mng raisins—W W. 0’?— +tr~c 3.13 2. I Consider an ideal gas at 25 °C in a 1.0 liter bulb connected to an evacuated volume of 4.0 liters by is closed valve. Now open the valve. letting the gas expand isothermally into the largervolume. Forthis expansion.givethesign of: q w AE AH AS AG 2311-0 so,bE=At-l=0 o 0 0 O + - (0 Put: =0 321,0 036': c2) .. A A§5=cb+uo a “a 4640 be dessert—T S. v As>o we Aer-«nun a O - Ci" 3. Which of the following statements is true (T) or false (F): (a) All real processes are reversible F Pi LS-E.‘ (b) In an reversible cyclical process, the system returns to its original state. but 3 -' ' the universe does not. F IQ L8 5 (c) All spontaneous processes increase the disorder of the universe mu‘e 4. If mL of water at 275 K is mixed with 30 mL of water at 375 K. what is the ﬁnal temperature T (in degrees K) of the mixture? Note: water has density = 1 gimL. and has specific heat = 4.18 Jl(oC g) Qawat m '5- % 0.00 L 5 sorta/mmm>m~gm= -50m4'9/maw-m~cmms) 3 T+= 30m :9 W '—' Page 2 ,tsrry 152C 5. Consider the following reaction sequence: ; (1)2A ——)B Ll (2) B —+20+D '2 (3) E —)o in teims of the enthalpies of the individual reactions (H(1), etc), write an expression for the enthalpy of the following net reaction: 2A —) 20 + E :2 A a £3 hm B’ “7’ 2c, ~12! FWD new w mm a new —Aitt2>\ 6. Consider the gas-phase reaction 02 (g) 4) 20(9) Predic‘ the Sign Of AH" and 458° for this reaction? Under what conditions of temperature (much higher, much lower} would the reverse reactiongoocur spontaneously? "3 All?» tena— imcwqgtnj ti or: 10101.13 or?” \$3013 3&8 col" {L0 WW5 7'. At what temperature does bromine boil (P= 1 atm) ? Br2(|) —> Bug) The enthalpy oi vaporization is AH°= 29.0 kamole, and the entropy change is AS" 2 8'50 J!(K mole) Again»? AS” =0 3:20 2mm g "I": #5:: GMT/ma M333“ 3. For the chemical reaction A —> B. give the temperature conditions for spontaneity for each of the following cases (i.e. spontaneous at all T, at no T, T high or T low) i {aJAS<0 and AH <0 lbw ﬁrm? I L] {b)AS>0 and AH <0 an HmPS (c) AS<0 'and AH 3'0 no Ht“? (d) AS>0 and AH >0 V113“ HWTFS 5 Version .-'/ /. . Chemistry 1520 Page 3 9. The equilibrium position of an endothermic reaction will shift toward reactants) with increasing temperature while for an exothermic reaction the equilibrium will shift toward the (products Circle correct response. 4 10. For'lfthe following values of AG", give the corresponding values for the equilibrium constant K (K=1, or K >1, or K < 1) AG°=0, K_4-_? 3 AG°<0, KA? I AG°>0, Kg? 11. In Boltzman‘s formula for entropy ( S = klnﬂ ). what does 0 represent? Why do more simpler molecules have smaller values of standard entropy 8° ? - —.- 4i 0? mimsi-acl-cs cwegpor‘din “to Wm Sin“ sampler molecules - how: WV pogc’lw‘!‘ Yoth rial why-abortch mo’n‘ ovxs : (ﬁnder mummies} 12. If ASS“ = - ASS”, then the system is at equilibrium. Oi z‘huilibﬁom Assn” = A3919*AS‘“"=O E «30 Agsurﬁ'Agﬂs Version / / x Chemise-2y 152C - Page 4 ll. QUANTITATIVE: Do all four [4} of the following {subtotal = 52 pts) 1. The heat capacity at constant pressure-of (302 is Cp = 38.25 JI{K mole). If 80.0 grams of 002 is copied from 175 °C to 55 °C at a constant pressure of 500 atm. calcuiate q, w. AE and AH for this process. I (goswz Amok 73 [Riga/totes I L‘Ibitbij Arie 554%”: "’30 5-” “CF 0T :(‘msl 3%.ZLS3C-l2ﬂh :— - 8 awe : W::‘l>£xt: 15V = £— 6m}(—3,550Q(\m933 -_~ |3l3.3> elbgi LTI —: *Z-BUHLT *} i-Q‘i‘L—I— : 2. hither: 1.00 liter of 0.50 M Ba{N03J2 at 25.0 "C is mixed with 1.00 liter 010.50 M Na2504 at 25.0 “.C in a calorimeter, a white solid BaSO4 forms and the temperature increases to 26.5 °C.i The heat capacity of the solution is 4.18 301°C 9). (Neglect the heat capacity of the calorimeter. and assume that the solution has a density of 1.0 glmL) Calculate the enthalpy change ﬁat-1%.. for this reaction per mole of BaSO4 formed. heat- absovlmidL a mCAT . k ' \ mL- it ,_ mass 1’ iDOL-t-itCDOL 1* 2L “‘(EE' -' “Mb ' 2000‘) m a ass—35.0 21.5%. : acmgﬂiigf/Soc305ﬂ 21351103" LW1W.d Mm (\m s: - 17.5%? I Alt “.: 43.5:qu Pf:m0'-¢ ‘L(‘l6_vﬂotﬁ a: -- L.- VersioniB ' . Chemistréy 152C Page 5 - 3. Calculate AH°rxn for the following reaction: 4NHa(g) + 702(9) —> 4N02(g) + eHzoa) The AH“; values (in kJr‘mole) are: NH3(g) N02 {9) H20 (I) - ~ 43 +36 - 275 : g mud-s ’.1 WWW-{:5 iEwatoMLoL—aweﬂ * [Lima J‘ j‘wﬂ 450m h (—I‘vrﬂ 4. Conaider the following reaction: Fe203(s) + 3H2(g) _, 2Fe.(s) + 3H20(g} Assdming that AH" and AS" do not depend on temperature. calculate the temperature at which K=1.00 for this reaction. The standard enthalpies of formation and standard entrdpies are: AG" :0 Men [:1 AH" (kamole) S°(JI(K mole) Fézoae) -834 +85 0 F A % :TA S Fe (3) (0) +24 T = 1—5}. H2 (9) (0) +137 133 ° H20(g) -235 +175 ' F H": mm“ Jr éL—aastj a [-33% “1 3(0)] -= lac! ELY/we- Cam + 30%)] {\$6 + 3W) "- “Mk/mote I 7" Eiagw -: Ho'th Version ...
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exam_answers_Exam_1_key - CiHEI'H‘IISTRY 152A HOUR EXAM...

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