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Unformatted text preview: \/ This print—out should have 8 questions.
Multiple—choice questions may continue on
the next column or page — find all choices
before answering. LDE Stat Thermo Theory 001
001 10.0 points
When calculating positionai entropy using the
Boltzmann formula (3 = it In W), which of
the following statements is / are true?
v/ I) An experimentally determined value of
W will be less than the ideai value. II) For the same number of molecules at ab—
solute zero, the experimentai value of W
for. HP will be greater than the expert»
mentai value for CO. III) At absolute zero, the positional entropy
of a group of molecules with one orienta»
tion will equal zero. 1. II only 2. I only 3. I, II, III
, III correct 5. n, In
6. I, II 7. III oniy Explanation: Statement I is true because ideal values
assume that IMF aren’t present and therefore
don’t inﬂuence the likelihood of a moiecule
adopting a particular orientation. Statement
II is false because HF has a stronger IMF
which thus more dramatically perturbing the
value of W. Statement III is true because I
raised to any power is i and the natural log of 11s 0. LDE Stat Thermo Energy 001
002 10.0 points Assuming vibrational modes are excited,
how much internal energy would be associ— . ‘i ., 5 ﬂ L '3‘ \J " a
' ' ‘31:.
. e» Version PREVIEW — Quiz 6 m hawkins —— (53755) 1 ated with just the vibrational motion of 10
molecules of 002? @0kT correct
2. BOkT
3. 15kT
4. 40kT 5. 45kT Explanation:
The energy of any given mode of move . merit for any given atom or molecule is equal to 1/2kT. Since carbon dioxide has 9 to—
tal modes, 3 of which are translational and
2 of which are rotational (because it is lin»
ear), it has 4 vibrational modes. Since there
are 10 moiecules and 4 modes, each of with
are worth I/ZkT, we have a total of 20kT in
internal energy. LDE Stat Theirmo Entropy 001
003 10.0 points If you had 1 mole of HF molecules, each
of which had two possible orientations, what
would their total theoretical positionai en~
tropy be at absolute zero? W I I
1.9.57x10 24JK 1 So; 1%,, g 2.461.}vK‘1 .
era 7, 3. 7.65 x 10—22 J  K"1 4. 5.76 J  K“3L correct Explanation:
s = almost) we em = 5.76 J . Krl LDE Internal Energy 001
004 10.0 points
Which of the following statements concerning
internal energy is / are true?
I) If the expansion work is small, AH and
AU are close in value.
ii) The internal energy of a system is equal Version PREVIEW — Quiz 6 — hawkins  (53755) to g at constant voinrne. III) Assuming no heat is exchanged, when
pressure—voiurne work is done on the sys—
tem, AU is positive. 1. I, III
2. II, III
3. Ionly 4. I, II
5. II only 6. III only 91:, III correct
xplanation: Statement I follows from the identity AH =
AU + pAV, because pAV is the expansion
work. Statement II follows from AU = q a w,
"because to z 0 for processes that occur at
constant volume. Statement III also follows
from AU = q + in, because w is the pressure
volurne work. (Note: for reversible processes, expansion work and pressurevolume work are
identicai.) LDE Internal. Energy Cale 001
005 10.0 points If a man is jogging and releases 800 kJ of
heat and does 200 kJ of work, what is the
man’s change in internai energy equal to? 1. “600 kJ k3 correct
3. 1000 Ltd 4. 600 kJ Explanation:
AU = q+w 2 —800k5 + —200kJ =
~1000 kJ LDE Ranking Entropies 001 10 006 10.0 points
Bank the following systems in terms of in: creasing entmpy: H (D8 \ gr” a) 1 H101 of pure ice
b) 1 mol of water with I moi of salt dissoIve
in it. c) 1 mol of pure waterhi IOUJ l.b<c<a @ < c < b correct 3.b<a<c
4.a<b<c
5.c<a<b 6.c<h<a Explanation: Entropy increases as systems go through
endothermic phase transitions and when there
is more matter or more dispersed matter
present. LDE Entropy Change Gate 001
007 10.0 points If a given system releases 900 J of heat,
what will A5 of the surroundings be if this takes place at 27 CC?
M in) .th J  KW} correct 1. 33.3J’K4 Explanation:
Heat released by the system will increase
the entropy of the surroundings by an amount equal to q/T, in this case
900 J _3
LEE Thermo 2nd Law Oak: 001 008 10.0 points Version PREVIEW m Quiz 6 — hawkins M (53755) Consider the condensation of water at
standard pressure at 10100. Even with
out knowing the exact values in ASWP and
Affmp, what can you say about the value of
Aﬂuniveme for this process? 1. ASumUeme would be a large positive num
ber. 2. asumme would be a iarge negative num»
ber. @Smmrse would be a small negative number. correct 4. ASmmrse would be a smallpositive nuns».
bet. ' Explanation: The process would be non—Spontaneous
(water doesn’t condense at 1 atm at 101 °C),
so ASmmme would be negative. We are near
the phase change temperature of water, so it
would also be small. ...
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 Fall '07
 Fakhreddine/Lyon

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