Answer the questionsa f regarding the diagram circle

141) The phase diagram for a substance is shown to the right. Answer the questions(a-f) regarding the
diagram:
(Circle one ): A B C
c) Estimate the melting point at 30 atm:
b) Circle the triple point on the graph.
f) A student wants to measure the enthalpy of vaporization at standard pressure. Why is this
impossible?
OK: does not undergo liquid -> gas transition OR vaporization occurs at higher P than standard OR
the liquid phase does not exist at 1bar; always in gas phase at 1atm 1/2
(Circle one ) -105 o C -15 o C -5 o C 50 o C 200 o C
d) The phase transition when going from A to B is called
( fill in the blank) : _________________
condensation
e) Which is more dense (Circle one): solid or liquid?
2
2
2
2
2
2

CHEM 230 W16 PREP E2 key p 35
n-pentane
C
5
H
12
isopentane
C
5
H
12
neopentane
C
5
H
12
bp 36
o
C 27.7
o
C 9.5
o
C
mp -129.8
o
C -159.9
o
C -16.6
o
C
a) Which compound has the highest molar
entropy at 25 o C ? (Circle one)
n-pentane
isopentane all are the same
neopentane cannot be determined
b) Which compound has the highest vapor
pressure at 0 o C ? (Circle one)
n-pentane
isopentane all are the same
neopentane cannot be determined
154) For parts a-d consider the data about the isomers of pentane (C
5
H
12
) shown below and to the right.
d) When the external pressure is lowered, the vapor pressure of n-pentane will become (Circle one)
higher the same
lower cannot be determined
c) Which compound will undergo the greatest change
in entropy when heated from -20 o C to 0 o C ?
(Circle one) n-pentane
isopentane all are the same
neopentane cannot be determined
3
3 3
3
3
182) Weather forcasters talk about relative humidity which is the ratio of the partial pressure of water in
the air to the equilibrium vapor pressure of water at the same temperature. The vapor pressure of water
at 32.2
o
C (90
o
F) is 36 mm Hg.
x
36 mmHg
= 0.9
x = 32.4 mmHg
P
water
= mm Hg 32.4
a) On a sticky, humid day, when the relative humidity reaches 90% and the temperature is 90 o F what
is the partial pressure of water?
b) Air at 90
o
F and 90% humidity is cooled to 31.0
o
C. Does any water condense? Yes No
Briefly explain your choice
The vapor pressure of water at 31.0
o
C is 33.7 mm Hg.
The partial pressure of water (32.4 mm Hg) is still less than the equilibrium vapor pressure of 33.7
(Circle one)
3

CHEM 230 W16 PREP E2 key p 36
P
1 bar
T
25 o C
P
1 bar
T
25 o C
P
1 bar
T
25 o C
P
1 bar
T
25 o C
A B C D
Place the letter or letters of the phase diagrams that match the description in each of the boxes below:
a) A substance that only sublimes (but does not melt and vaporize) under standard pressure.
b) A substance whose solid is less dense than its liquid.
c) The substance with the lowest standard melting point.
A , C
B
A
6
2 each
180) Consider the four phase diagrams A-D shown below.
209) Consider the carbon dioxide phase diagram.
a) True or False : Solid carbon dioxide melts at ~ 220 K
under standard pressure.
b) True or False: Solid carbon dioxide sublimes at a
pressure of 10 bar.