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Unformatted text preview: Chemistry 105bL First Letter of PLEASE PRINT YOUR NAME IN BLOCK LETTERS
1 1:00 am. Section Last Name Fall 2007 Name:
EXAM #3 November 6, 2007 SID #:
Professor Arieh Warshel Lab T.A.'s Name: Lab Day and Time: QUESTION MAXIMUM SCORE GRADER
POINTS Please Sign Below: I certify that l have
observed all the rules of
Academic Integrity while
taking this examination. Signature INSTRUCTIONS:
1. There are 5 problems on 9 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 1023 mol‘1 Universal gas constant R = 0.08206 L atm K" mol‘l
= 8.314 I [Cl mol" Faraday’s constant F = 96,485 C mol‘l K p = KART)“ ln k = —%(1T) + lnA —bi‘/b2—4uc Ifax2+bx+c=0thenx= 2
a PV=nRT
w=q§ AS=kln W
AG=4m§
AG=AG” +RTan
AG=AH—TAS
E=q+w
AG”=—RTaneq
E=hn=mc2
—A—f=—%+As kB = 1.38 x 1023 J/K l. (20 points) Consider the diagram of a potentiometric titration of an acid AH curve show below.
12.0 P D 8.0 » . , . .
solution 6 0 Egﬂzalence
in ﬂash: 4'0 2.0 5 10 15 20 25 30 35 4O 45
mL of 0.115 M NIOH added to flask. (a) You have three indicators (XIH, XzH, X3H) IH I‘ pKu
X I H red blue 9
XZH red colorless 8
X ]H colorless blue 9
dc where [H and Iare the protonated and ‘protonated forms of the indicators. Which
indicator will be the best one for our system? Explain. X5”. 716 Malicefur 75 W W 42" fbﬁ = g
g WAI‘M I3 7% Stunt 4.4 % Mug,» we WM‘IL 79 Jun/Yer. [H fit! 9/ We will Sin/#14)“ é/uc Wm} if ﬁe dri ﬁu/ solar“ is co/w/css (X, II), but we um' m % r'sf
aﬂumuce m0 blue iF Me dry/w 99/wa is M. (b) Is AH a weak acid or a strong acid? (c) One liter of solution of HCl
be added to this solution to reach pH = 7? has pH = 3. How many liters of 10'3 M NaOH should [\J
g BX3(s) g B*2 (aq) + 2x (aq) J‘ 2 5‘
Answer the following questions. ‘ in solution formed by adding 0.1 mol BX2 to 1.0 liter
of 0.02 M B”?
This MM is 43,60 74.), Df'J) M 745’ 3,
~ 2.
7 k3,: = [B 2’70 J 2. _ 2.
LOX/Eu: (5+ 0.0:) C)! 'J 2: 0.02 D ] 64nd alien/,9)»: /
1. (£1 7475 4 0.02 :0.”
“ 4 ° —/o
{x} giDx" ); : 7100 M
W ‘
Which of the ions ( * or B”) will precipitate first b (b) y adding X‘ to 0.1 liter of a
7 solution that contains 0.1 M of A+ and 0.02 M B”? °/% 2
X awn: «Kan 0"]: ﬁg: W: IMOISM K er
BY: 1c?” .w/Iu Dr]: (.o”;¢%3 f. .M 41'  Mil
. _ [32" 0.02. 7):”) a W?
A * W"”)(Pr“'fvh*¢ r} last“
(c) lfAX IS red and B 2 IS ye low, what will e the color of the system formed after
adding 0.5 moles of X“ to a liter of solution that contains 0.10 mole of A+ and 0.02
moles of B”? Explain. 0.54 » lX/o'laMl 5,, 414+ facials (MW 0512 >> 7X/0“M, So all Byprui’u'ﬁ/rs [ye/Aw Val + ye l/m’ = oral42¢ (ff, aalnkss SO/Uﬁan. 3. (20 points) (i) Which one of the following is not zero for an element in its standard state at 25“C?
(21) AG}?
(c) AH9
’ A S‘ > 0 /7 (ii) Dissolving ammonium chloride in water lowers the temperature of the system.
For this dissolving process S AH is negative and AS is negative A H >0 (a)
“do ‘Merm 12‘.
3 (b) AH is positive and AS is positive
(C) AH is negative and AS is positive (d) AH is positive and AS is negative (iii) The table shown below contains entropy values for four substances at 25”C. All
of the values are correct except one. Which one is incorrect? Substance S“ (J/molo K)
5 F2(g) 203
C12 (g) 1 15
Br2 (l) 158 was
12 (s) 117 m
'3 5.2%»
/2 (a) 203 5091(3) > 5;; since. at Me‘“&' (b) 115 A 4‘“ F
is 1‘ 0‘ 7’
(c) 158 —"Jj—' ' mm
5 “2(7) > 5;,0) >5.,/:) mm dim: 91" 1%.“ {,1 j“ M4,. ,;, 5 “1 mm in lira)! 7%,, in so/I‘al. (d) 117 (iv) (continued) The entropy of vaporization of (ASUQP) of an element, X, is 120 J/K mol while the
enthalpy of vaporization (AH‘Jap) is 60 kJ/mol. (a) Find the boiling temperature for X.
0 god": AH’TAS
AH = TAS AH
7— 25' 3
60/00 Jim!"
(20 Th"m€" = 500K (b) What will be the spontaneous direction of the evaporation process (liquid —> gas or gas —> liquid) at T = 2"K? Explain. 2/4 4 STD/4: Lei/"'3 [chit at 1")
Thus, 1—)? is no?" sfmfanems. What is the equilibrium constant Kp for evaporation at the boiling temperature? 435...: 0 : ~RTz‘ttk Alba
/<=/ (C) 4. (a) S (20 points) [Von/7241 Please evaluate the entropy change upon moving two atoms from A to B (each box can contain only one atom). . v 15%.“)
435:1, A; ’A.A/5=1AA,, A (EM/314793715 are Manéaf
ea! As 2 4.24m” 31" Circle "True" or "False" for each statement below. (b) (i) It is impossible to convert heat to work without losing some heat. True
When we clean our room the entropy of the universe decreases. True
Boltzman‘s grave stone has the formula E = mc2 on it. True
q is a state function. True
Irrersible PAV work gives us the most efficient
machines. True True The entropy of graphite at 0 K is zero. False False False False False False OD 090 g = Qsenzzzzrk'Déoﬂ/e) 4. (continued) 6 (c) Describe very qualitatively how the light energy is being stored in the first step of the vision process. 5. (20 points) \
(i) What is the sign of AS for melting of ice? . 71m 1‘3 m 19:44.. 4&0th I3I 5741417541. duh/,1
Q So ‘Men as mm «(aMr [a 7% /W. 3' ASH!" "' A :4 ' 43:0”; >0
/ 3" C713 cart/3V4. M (ii) Can you have a eaction with S < 0 if we have a system that is completed isolated
from its surroundings? Explain. Atr=AH—72>S ‘
ill A340) Mon 4340“ a»? 4‘40 Hedi/<0) 7 Which Cann'f W in an I‘SohM S/a/em.
0R AH' 0 4v 4» Mia—79b S/ﬂ‘uu
I‘ A3<0, Hm 0—71554; >0 $6 @4— >6, I‘s MWﬁn¢m, (iii) Consider the reaction A(g) —> B(g) where AG” = 10 kJ/mol at 298 K. What will be the
direction of the reaction where P A = 1 atm, and PB = 1 atm? (Show your work.) Acr" = [0 NM": 473mg véé" —/0¢J/m.[" _ _¢
= "*" = ~ .0
7 Ink RT (5. 3m J'WVIC'Qﬁﬁk) f K= (4”: 0.0; 4/ ...
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This note was uploaded on 07/13/2008 for the course CHEM 105BL taught by Professor Warshel during the Fall '07 term at USC.
 Fall '07
 Warshel
 Chemistry

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