Exercises 539109.The boiling points of HCl, HBr, and HI increase with
increasing molecular weight. Yet the melting and boiling
points of the sodium halides, NaCl, NaBr, and NaI,
decrease with increasing formula weight. Explain why the
trends are opposite.
110.The structures for three molecules having the formula
C 2 H 2 Cl 2 are
the planet Mars at a temperature of 100°C, they will
gradually disappear by the process of ________ and form
a ________.
*117.The van der Waals constants (Section 12-15) are a
19.01 L^2 atm/mol^2 , b0.1460 L/mol for pentane, and
a18.05 L^2 atm/mol^2 , b0.1417 L/mol for isopentane.Describe the intermolecular forces present in each of
these compounds and predict which has the lowest boil-
ing point.
111.Are the following statements true or false? Indicate why
if a statement is false.
(a) The vapor pressure of a liquid will decrease if the
volume of liquid decreases.
(b) The normal boiling point of a liquid is the tempera-
ture at which the external pressure equals the vapor
pressure of the liquid.
(c) The vapor pressures of liquids in a similar series tend
to increase with increasing molecular weight.
112.Are the following statements true or false? Indicate why
if a statement is false.
(a) The equilibrium vapor pressure of a liquid is inde-
pendent of the volume occupied by the vapor above the
liquid.
(b) The normal boiling point of a liquid changes with
changing atmospheric pressure.
(c) The vapor pressure of a liquid will increase if the mass
of liquid is increased.
113.The following are vapor pressures at 20°C. Predict the
order of increasing normal boiling points of the liquids,
acetone, 185 torr; ethanol, 44 torr; carbon disulfide, CS 2 ,
309 torr.
114.Refer to Exercise 113. What is the expected order of
increasing molar heats of vaporization, Hvap, of these
liquids at their boiling points? Account for the orders.
115.Refer to the sulfur phase diagram on page 536. (a) Can
rhombic sulfur be sublimed? If so, under what conditions?
(b) Can monoclinic sulfur be sublimed? If so, under what
conditions? (c) Describe what happens if rhombic sulfur
is slowly heated from 80°C to 140°C at constant 1-atm
pressure. (d) What happens if rhombic sulfur is heated
from 80°C to 140°C under constant pressure of 5 10 ^6
atm?
116.The normal boiling point of ammonia, NH 3 , is 33°C,
and its freezing point is 78°C. Fill in the blanks. (a) At
STP (0°C, 1 atm pressure), NH 3 is a ____. (b) If the
temperature drops to 40°C, the ammonia will ____
and become a ____. (c) If the temperature drops fur-
ther to 80°C and the molecules arrange themselves in
an orderly pattern, the ammonia will ____ and
become a ____. (d) If crystals of ammonia are left on
C CH 2
HCH 3
CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 3pentane isopentaneC CCl
H HCl
C CCl H
H ClC CCl H
Cl H(a) Basing your reasoning on intermolecular forces, why
would you expect afor pentane to be greater? (b) Basing
your reasoning on molecular size, why would you expect
bfor pentane to be greater?CONCEPTUAL EXERCISES*118.Iodine sublimes at room temperature and pressure; water
does not. Explain the differences you would expect to
observe at room temperature if 5.0 grams of iodine crys-
tals were sealed in a 10.-mL container and 5.0 mL of
water were sealed in a similar container.
*119.Referring to the phase diagram for carbon dioxide shown
in Figure 13-17b for approximate values, draw a heating
curve similar to that in Figure 13-15 for carbon dioxide
at 1 atmosphere pressure. Draw a second heating curve
for carbon dioxide at 5 atm pressure. Estimate the tran-
sition temperatures.
*120.A popular misconception is that “hot water freezes more
quickly than cold water.” In an experiment two 100.-mL
samples of water, in identical containers, were placed far
apart in a freezer at 25°C. One sample had an initial
temperature of 78°C, while the other was at 24°C. The
second sample took 151 minutes to freeze, and the
warmer sample took 166 minutes. The warmer sample
took more time but not much. How can you explain their
taking about the same length of time to freeze?
*121.Consider the portions of the heating curves shown here.
Which compound has the highest specific heat capacity?Heat AddedTemperatureCompound ACompound B