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Unformatted text preview: Last Name First Name Lab Sec. # ; TA: ; Lab day/time: Andreas Toupadakis, Ph.D. Fall 2006
CHEMISTRY ZC
Section A
EXAM 2
Instructions: CLOSED BOOK EXAM! No books, notes, or additional scrap paper are
permitted. All information required is contained on the exam. Place all
work in the space provided. If you require additional space, use the back
of the exam. A scientific calculator may be used (if it is a programmable
calculator, its memory must be cleared before the exam). This exam has
11 pages total. (1) Read each question carefully.
(2) For Part I there is some partial credit. There is no partial credit given for part II. There is partial credit for part III.
(3) The last 2 pages contain a periodic table and some usaful information. You may remove them for easy access.
(4) If you finish early, RECHECK YOUR ANSWERS! 13.a b 14. a b
U.C. Davis is an Honor Institution /25 16.a@ c 17. a b
18. a
19.a b c Possible Points # 112
# 13—21
# 22 (15 points)
# 23 (25 points) (2 points each) (4 points each) 21.a b c /100 @ 0'
n @n
D_Q_Q_O_@
[email protected] Total Score (100) £5
0'
n0
an.
an CL 13 21 fatal points: Name Exam 2 (Page 2 of ll ) Par'T I: Concest (2 poinTs each) Some parTial crediT is available 1. CompleTe and balance The following reacTion: Kcs) + 02(9) a kolm 2. CompleTe and balance The following r'eacTion: + 01(5) +1HZOU) * Cc: L‘qu T lOHYUqx \ \—\z (gl 3. CompleTe and balance The following reacTion:
a Al(s) + 302(9) 6 ‘1 (M7, 0 v, (a
4. CompleTe and balance The following reacTion:
5iC4(9) + 1H2(g) —> Q: (0 Jr q \x 02 (3x 5. Give The Two reasons why The compound NF5 does noT exisT buT PF5 does. (0\ Nilvozéev‘ glow iS §WOpg€r *Mom pMogplnovug
glow. \Vl \Allvozevx C09: “tell“Moms Woueol be
Grounded. gem «foam. ,, .. Lb\upﬂ glow \nog d {\O. Ovcxleob‘eﬂ ’Qo‘r bomdlma‘ N (3er incl. 6. WhaT is aqua regia?
l\ \AAKXTKNG, 0{ Come. l\CSZCc1q\ CLViG Come. HNOacq“
\\A Q :Sil Yo¥<0 by voeuwe. 7. Is The compound N204 paramagneTic or' 8. Draw clearly The sTr'ucTur'e of P4010. \ Name Exam 2 (Page 3 of ’l 1) 9. Write the balanced chemical equation for etching glass made from SiOz with
hydrofluoric acid, producing silicon tetrafluoride gas. glolfs’) {7 L\“C(0q\ ~———> <iCu(3\+ illeCzl 10. Which of the three acids: H3POZ, H3P03 or H3PO4 is a diprotic acid? HSPOg 11. When chemists study chemical reactions, they ask three fundamental questions. What happens?
To what extend does it happen? Tl" e YW‘ 03 ‘l vaw' c. S How fast does it happen? k; We ‘ C C § Each of the last two questions can be answered with one word, indicating the field of
science that gives the answer to the question. Give the words. 12. Give the units of the rate constant for a third order reaction. Name Exam 2 (Page 4 of 11) Part II: Short Calculations (4 points each)
No partial credit (right or wrong) 13. Consider the reaction: 4 PH3(g) —> P4 (9) + 6 H2(g)
If the [H2] increases from 0 M to 3.0 M in 60 sec; What is the rate of the reaction? What is the rate of disappearance of PH3? a. rxn rate = 0.0083 Ms'l rate of disappearance of PH3 =  0.033 s“ b. rxn rate = 0.0083 Ms rate of disappearance of PH3 =  0.033 Ms1 C. rxn rate =  0.0083 Ms" rate of disappearance of PH3 =  0.033 Ms"1 d. rxn rate = 0.0083 Ms'1 rate of disappearance of PH3 = 0.033 Ms’1 e. rxn rate = 0.0083 Ms'1 rate of disappearance of PH3 =  0.033 Ms'1 BCRIJ \ (%.O~O)N l— ._...__——— — : "‘ QQ'\€ OE disguPP. of Wk 1 ’ Li (WV‘ YO“) C ’L‘ x 0' Dog? :’ 00%; M Sp" 14. For the reaction: CZH4Br2 + 3KI —> 62H4 + ZKBr‘ + KI3
Initial rate data at 60°C are: [CZH4Br2] [KI] A[KI3]/At (M/min)
0.500 1.80 0.269 0.500 7.20 1.08
1.50 1.80 0.807 The rate law is: a. rate = k[Czi‘i4Bf‘2][KI]3
b. rate = k[KI] c. rate = k[C2H4BI‘2][KI]
d. rate : k e. rate = k[C2H4Br‘2] Name Exam 2 (Page 5 of 11) _____________——__________._._—————————— 15. DaTa for The reacTion: A + B —> C are given below. Find The r‘aTe consTanT for‘
This r‘eacTion. ExperimenT [A] [B] IniTiaI raTe (M/s)
0.030 0.060 2.5 x 10'5
2 0.030 0.020 2.5 x 10'5
0.060 0.060 10.0 x 10'5  k = 2.8 x 10'2 M‘ls‘1
. k : 2.8 x 10251 . k = 9.2 x10'2M'ls'1 . k = 4.5 x IO'ZM'Zs'l . k = 4.5 x 10‘2Ms'1 NQGO'D Qale 4: k [931(33'30: PCNXI Av» l4: (20AM [A31 '5 ~i '
\ : 1.6ﬁl0 NS : 1‘8X\O Zquq.
0.0301 M1 16. The reacTion A + B —> C + D is second order in A, and zero order in B. The value of k is 0.012 M_1 min—1. WhaT is The r‘aTe of This reacTion when [A] = 0.125 M and [B] =
0.435 M? a. raTe = 6.2 x 10'5 M min'1 b. raTe = 1.9 x 10" M rnin'1 c. raTe =  3.5 x 10'5 M min'1 d. r'aTe = 6.8 x 10'20 M min'1 e. raTe = 5.2x 10'3 M min'1 (L _
QOSVC ': L< Z (0.0\'L [\A lw;m'l\(0‘\1§M\L: LO) XlO—ll vwvx—l 17. The firsT or‘der‘ reacTion A —> producTs has TU2 = 150 sec. WhaT percenT of The
sample remains unreacTed afTer 300 sec? a. 10%
b. 78% o
c.40°/o A’ETQY \§O §€C M €0/o cmveocled
d. 25%
e. 30% ‘
l\/€\€Y lgo §€< Oddlliomové N Lgouo :_ Z
3 QCK vaeoclecl. Name Exam 2 (Page 6 of 11) 18. 19. If a reaction is first order with a rate constant of 5.48 x 10'2/sec, how long is
required for 3/4 of the initial concentration of reactant to be u5ed up? a. 67.8 sec , b. 3.69sec l;:’)_t”L 31X 0.692 :QX osqz c. 25.3 sec k é‘qexbn, A
d. 27.6 sec C
e. 98.4 sec ‘: 1§_3 Sec A reaction is first order. If its initial rate is 0.0200 M/sec and 25.0 days later its
rate is 6.25 x 10'4 M/sec, then its halflife is: Cl. 'l'1/2 = day b. T1/2=2~0d0Y5 Q t [4 Q0 :0.0ZOO/Vl<": L C. 11/2 3 days )
d. 1'1/2 = days 2' m2 = 5'0 days A4 ‘l: 15‘0 dogs ) Q; :6_'LCX\OPuMs" é
Cir) o 2
A / :H ~a A 30.4.». A» \mm 0:925:
[Flt (.h 5 o. (L,
20. The firstorder reaction A —> Products has a halflife, rm, of 55.0 min at 25 °C and
6.8 min at 100 °C. What is the activation energy for this reaction?
a. 34.2 kJ mol'1
b. 25.8 kJ mol" T ~: K (€V1)‘ 0 Win
c. 78.3 kJ mol'1 ’
d. 38.9kJmoi1 ’ﬁ :l’(~%.\§ k, (ﬁlth: 6.8 wn‘m
e. 12.6 kJ mol'1
“QM ‘IQ : éu LP\ {II/1 7‘0.qu )’€M (Ll/137’ 1 £3— l .\__\
in a “ll 1: ) l< ({M‘ a T1, 7.
21. In the first order, reaction A —+ products, [A]: 0.400 M initially and 0.250 M
after 15.0 min, at what time will [A]: 0.200 M?
a. 45.6 min
b. 67.5 min ‘ ‘
c. 89.8 min t '0 , [A10 ‘ O'LlOO’V‘
d. 34.5 min : \g~ ~ pig 1 0‘ L
e. 22.1mm E 0 \MM) C {— 750 M £0018
k .16 _ “e Clﬂo
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C if) e
£30, C030 '1 OvLiooM
t4, [Quorum/M A; 6:124 w.“
_ l b [Mo
E _ k CM f Name Exam 2 (Page 7 of '14) Par'T III: Long Answers Please show all work for calculations  ParTial crediT may be given 22. (15 poinTs) Given The following informaTion for The r'eacTion: 2N0 + Oz ——> ZNOZ RATE (M/s)
0.050 a) DeTer‘mine The r‘aTe law expression for The reacTion. b) DeTer‘mine The value of The r'aTe consTanT.
c) DeTermine The raTe of The r'eacTion when [N0] = 0.020 M and [02] = 0.020 M. a) RaTe law expression: RaTe = k LN [0331 6“). ’l ow) H glnows ’lml mdev‘ dependence On E011
éfp. ’1. gm} 2. ‘* lsl OYdev depemdemu 0“ [N03 — Ll '7— l
b) RaTe consTanT: k  l.°>><\o N g Av“, (\[VPﬂlw’t’W‘l Q : [NOXEQAL So ’Qov ‘91“). i I
O'Ogo 3 1" CO'OHqAQOOZOVL "‘3 \K : LEXIOI‘ “(29" c) RaTe of r‘eacTion: Rafe =O.lO.SAi
, I L
Qule : (l3 ’XIOL‘ M.Z<"» (doze/vi) (0.010 M\ : : O.lO M<ﬂ4 Name Exam 2 (Page 8 of 44) 23. (25 poinTs)
Formic acid (HCOOH) decomposes in The gas phase aT elevaTed TemperaTures as follows:
HCOOH (9) —> 602(9) + Hz(9) The decomposiTion reacTion is deTermined To be firsT order. A graph of The parTial
pressure of HCOOH versus Time for decomposiTion aT 838 K is shown as The Top
curve in The figure below. 300 Pressure (Torr)
HCOOH
150 0 500 1000 Time (3) When a small amounT of solid ZnO is added To The reacTion chamber, The parTial
pressure of acid versus Time varies as shown by The lower curve in The figure. a) Using The above graph calculaTe The firsTorder raTe consTanT for The
decomposiTion of formic acid, before ZnO is added. b) WhaT can you conclude from The effecT of added ZnO on The decomposiTion
of formic acid? c) The progress of The reacTion was followed by measuring The poTenTiaI
pressure of formic acid vapor aT selecTed Times. Suppose ThaT, insTead, we
had ploTTed The concenTraTion of formic acid in uniTs of moI/L. WhaT effecT would This have had on The calculaTed value of k? d) The pressure of formic acid vapor aT The sTarT of The reacTion is 3.00x102
Torr. Assuming consTanT TemperaTure and ideal—gas behavior, whaT is The
pressure in The sysTem aT The end of The reacTion if The reacTion is 100%
yield? If The volume of The reacTion chamber is 436 cm3, how many moles of
gas occupy The reacTion chamber aT The end of The reacTion? e) If AH ° for The overall reacTion is 15 kJ/mol and The acTivaTion energy E,
for The reacTion is 184 kJ/mol, skeTch an approximaTe energy profile for The
reacTion, and label AH °, Eu, and The TransiTion sTaTe. Exam 2 (Page 9 of 11) Name
3 l a) Rate constant = \. LI x 10‘ g , It [/1 b) Conclusion: k F FYOW HA5 aYopM {171 : 500 S ZMO OC+S Ug <1 CU¥U€~I§¥, c) What effect? Nomei
D. X 300 Eovv 1’— GOO {:0Yv. d) Pressure =
Moles = goomo" woees ' *
u w I .
PV :WPT A); W: QT (Cogli Ldtw \(8ggk) Wo‘ek 3
215.00 XIO macQ1 S. e) The reaction profile: TYOW§i #80“ C +Q\'C => ng‘rf’m‘mu 6
emevgj Name Exam 2 (Page 10 of 11) Some useful equations and constants: PLEASE NOTE: Important values and equations required for calculations are given
with the respective problem. The following may or may not be of any use. Constants: R = 8.3145 J / mol K NA = 6.022 x1023 latm = 760 torr R = 0.0821 L atm / mol K h = 6.626 x 10'34 J s 1nm = 10'9 m 1 L = 1000 cm3
Equations: Slope : Ay/Ax TK = Toc + 273.15 T01: — 32 = 1.8 ToC Eu AG°=AH°—TAS° AG=AG°+RT1nQ AG°=—RT1nKeq k=AeW PV =nRT 1n:_I=E_a[i_i] 2 R T2 T]
We = kiAJO = k [A], =— kt + [A10 11 = We = k[A] 1n[A], = —kt+ln[A]O ti = 23:93
rate = k[A]2 L : kt + 1 ti = 1 [A1, [A10 2 k[A]0 H 01m €32 TS H.3552232233Egécgoméow.E33595 5% w: 2; o:
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This note was uploaded on 07/03/2009 for the course CHE CHE 2C taught by Professor Nasiri during the Fall '07 term at UC Davis.
 Fall '07
 Nasiri
 Chemistry

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