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Unformatted text preview: ()CMDQJ Z 003 Chemistry lOSbL First Letter of PLEASE PRINT YOUR NAME IN BLOCK LETTERS
11:00 a.m. Section Last Name Fall 2004 Name: EXAM #3 October 26, 2004 Last 4 Digits SID #: Professor Arieh Warshel Lab T.A.'s Name: Lab Day and Time: Please Sign Below: I certify that I have
observed all the rules of
Academic Integrity while taking this examination. Signature INSTRUCTIONS: 1. There are 5 problems on 10 pages in this exam. Please check to see that you have a complete exam. 2. Please show all of your work to receive full credit. 3. You must use ink. Do not use a pencil. Useful Physical Constants and Equations: Avogadro‘s number N = 6.022 x 1013 mol"
Universal gas constant R = 0.08206 L atm K“ rnol'l
= 8.314 I K" mol"
Faraday's constant F = 96,485 C mol'l
K p = K C(RT)” Ea I
Ink:T ;] + lnA —b:: b1—4
Ifax2+bx+c=0 thenx=—2a—ac— PV=nRT.
w=q§ AS=k In W
136:an
AG=AG° + RTan
AG =AH—TAS
E=q+w AG” = —RT 111K“, 1. (20 points) A buffer solution contains 0.10 M of HF and 0.20 MNaF (here we refer to the initial
concentration before equilibration). The K_ of HF is 3.5x10“. \5 ..
a) Calculate the pH ofthis solution. P 13* = 7&7 (5 5V0?
[FJ 1‘ 3' 5‘4
79H 3' Pkg, 4— 1Z9? 10 b) 50 mL solution ofO. 10 M HCl has been mixed with 10 mL of 0.20 M NaOH. What is the
pH of the resulting solution?
ya 4~ Neal? 9 Mac! + #,0 95533 m .] 2.0»? '3 MI m ———'.—r ¢
“ 3.0mm mu!
+3 = Egg—1" = 0.050 ’1
[H " 5mm;3 L PH: 130310050)?” ['30 2. 0 (continued) A reaction that gives off heat under conditions of constant volume has:
i) AE° > 0
ii AB” = 0
® AB” < 0
1v AH" > 0 v AH°= 0
AH°< 0 g) The third law of thermodynamics states that: i) AE = q  w
ii) AH = AE + paw
iii) AG = AH — TAS @ S=Oat0”'K v) none of the above
h) If W is the number of ways of arranging objects in space, the entropy S is:
i) not related to W
ii) proportional to W
@ proportional to in W (or log W)
w) proportional to e‘" (or 10‘")
v) proportional only to the Boltzmann constant k
i) For the reaction, '2 H.z + I2 = 2H1, the quantity [ Circle the correct answer. True or [Hzlllrl is always equal to the equtlibrtum constant, 2. (20 points) Circle the correct answers. a) A spontaneous reaction is one in which:
i) AH” < 0
ii) AH° = 0
iii AH" > 0
AG” < 0
v AG“ = 0
vi) AG“ > 0
b) A reaction that causes the system to become cooler as it proceeds has:
i) AH" < 0
ii AH” = 0
ﬂ, AH" > 0
IV) AG° < 0
v) AG° = 0
vi) AG" > o
c) At equilibrium, AG' ._. $6,. " 7L K735” Q
i AG < 0 _ 0
ii AG=O ) dM 0: 06' +RTAK
iii) AG > o (y'
m mm M75 04": ﬁremen}:
v) AG° = o 1"
vi) AG” > 0
d) The freezing of water is a process in which:
i) AS° > 0 ii) AS°=0 [53 Man Wm M67?
AS°<O e) The reaction of PCls(g) —> PC13(g) + Cll(g) has: 6) AS°>0 lM9JZ/JM3 ii) AS° = o m) 4M“ M“ and5w"
. 3. (20 points)
Given the following information:
W5 (5) :3 Mn‘2 (aq) + 5'2 (aq) K”, = 1.4 x 10‘”
ZnS (s) r: Zn"2 (aq) + S'2(aq) K.,, = 1.2 x 10.23
Answer the following questions: a) What will be the solubility of ZnS in pure water? ZnS 3; gr!” +8;
)6 K
(”‘IfS 0,6 ”07L (bid/M here.) K9,): XL =/LX/a 13M;
X .:: 5.5)00 Iz—M .—I' b) Which ion (Mn+2 or Zn”) will precipitate first by adding 5" to a solution mixture of
0.040 M Mn+2 and 0.0010 M Zn”? Show your work. [MSW—c“ Mn1++5r £7,31 £72+ _ k3 = I 1"” 3 2"” 8‘2
’4' "1+ 2 P
kf‘f: I'MI  riM JIS J I. Z”... ._=23 (0 “”‘QCIJ than {(5.0%) 3 __
[*7 575’ :C’VJ [32’] ”4’0”
3 : . )(l 4&4 [3 J15 Wat/é
4.92,,“ W5 AIM. “W )I 1‘ F\ [*1 7' . A no. .1 l... 5. (20 points) Consider the X10) —> X?(g) vaporization process. For this process AS“ = 105.0 J/K mol,
AH" = 22.0 kJ/mol. a) What is the boiling temperature of M2 at 1 atm? a5! . 0 Moi»? 7— : ms)!“ M" 5. J/OK b) What will be the sign of AG for boiling of X2 at 50°K and what does it tell us about the
direction of the vaporization rocess'? AG: 2?)00 233— (SOHC’OSJZKWJ)
Ad: Ma, 7572 3M4 : /é.82é,J'/nu/" c) What is the equilibrium constant for the vaporization process at the boiling temperature? . ... _,.‘. 1355—: pawn/2' = 0 we aﬂwmm
ink =0
K =/ d) What does the positive value of AS” tells us about the relative order of the system? (Explain) X147) is ”MY?! a/x'sMrtl Vzém, {1&3}. 04> X2. (2) /‘5 1470?. draélwl ﬂaw rill/f) or) X21?) f5 mm rm “MM Yaw. ...
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 Fall '07
 Warshel
 Chemistry

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