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University of Waterloo Chemistry 254: Thermodynamics
Term Test 2 Tuesday 6 July 2011 8:30-9:20 AM
NAME
.................................……………................................
I.D.
................................................…............…………..…
INSTRUCTIONS
(1) Answer ALL the questions, and do the easy ones first. The
weight of each question is
given in the table below.
(2) A standard, non-programmable calculator is allowed.
(3) Total time permitted for this examination is 50 minutes.
(4) The data sheet is given on the last page of this exam
paper.
NOTE
Be sure to present your work logically and neatly, and cross-off
any rough work that you do
not want the marker to see. Marks will be deducted for messy,
disorganized presentation.
SCORE
Question 1 /5
Question 2 /5
Question 3 /5
Question 4 /5
Total /20
Please hand in this exam paper. Be sure to PRINT your name and
ID on both. WARNING: Cheating in exam is considered to be the most
serious academic misconduct and is
ground for expulsion at the University of Waterloo. Don’t do
it!
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1. (a) Liquid water at 100C is in equilibrium with water vapour
at 1 atm pressure. If the
enthalpy change associated with the vaporization of liquid water
at 100C, i.e. H, is 40.60 kJ
mol-1
, what is G and S?
(b) Suppose that liquid water at 100C is in contact with water
vapour at 0.900 atm.
Calculate S and G for the vaporization process. Hint: Consider
the additional entropy
change for the expansion of the water vapour from 1 atm to 0.900
atm (assuming ideal gas
behaviour for water). Also assume that H has not changed in this
process.
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2. The melting point of water at 1 atm is 0C and the enthalpy of
fusion is 6.0095 kJ mol-1. The
boiling point is 100C and the enthalpy of vaporization is
40.6563 kJ mol-1
. The molar heat
capacity CP,m for H2O is 75.291 J K-1
mol-1
.
Calculate S for the transformation of H2O(s, 0C) H2O(g, 100C).
Express your answer
in J K-1
.
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3. (a) One mole of an ideal gas is expanded reversibly and
isothermally from 10 L to 20 L.
Calculate S. Express your answer in unit of J K-1
.
(b) One mole of an ideal gas is expanded reversibly and
isothermally from 1.00 bar to 0.100
bar. Calculate S. Express your answer in unit of J K-1
.
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4. Consider a system consisting of 1.5 mol CO2(g), initially at
15C and 9.0 atm and confined to
a cylinder of cross-section area 100.0 cm2. The sample is
allowed to expand adiabatically
against an external pressure of 1.5 atm until the piston has
moved outwards through 15 cm.
Assume that CO2 may be considered as an ideal gas with CV,m =
28.8 J K-1
mol-1
.
Calculate q, w, U, T, and S. Express your answers in J, K or J
K-1
, where appropriate.
END F TEST
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DATA SHEET – For convenience, you may tear off this sheet and
use it during the exam period.
There is no need to hand in this sheet at the end of the exam.
You may keep it or trash it.
Equations and Constants
Constants R = 1.9872 cal mol-1
K-1
= 8.3145 J mol-1
K-1
= 0.082057 atm L mol-1
K-1
= 0.083145 bar L mol-1
K-1
= 8.3145 Pa m3 mol
-1 K
-1 = 62.364 torr L mol
-1 K
-1
0C = 273.15 K
General equations dVV
UdT
T
UdU
TV
PT
PT
V
U
VT
For a (monatomic) ideal gas V
nRTP and 0
V
U
T
R2
5
n
CP and Rn
C
n
C VP
For a van der Waals gas 2
2
V
an
nbV
nRTP
and
2
2
T V
an
V
U
The thermodynamics magic square
T G P
V U S
A H
