Page 147 - Modern physical chemistry

138 Relationships between Phases

6.12 How many grams of urea must be added to 25.0 g water to obtain a boiling point elevation
of 0.200° C?
6.13 If the heat of fusion of acetic acid at its freezing point 16.6° C is 180.75 J If! , what is its
molal depression constant Kr?
6.14 Solid iodine in equilibrium with its pure vapor at 20° C has a vapor pressure of 0.202 torr
and a density of 4.93 g cm.J. If the pressure on the iodine is raised to 100 atm by mixing an
inert gas with its vapor, what is its new vapor pressure?
6.15 Calculate the osmotic pressure of a 0.130 m sucrose solution at 150° C.

6.16 Three solutions, 0.1 M NaCI, 0.1 M NaN0 3 , and 0.1 M AgN0 3 , were mixed. How many degrees
of freedom does the resulting system exhibit?
6.17 When does sulfur fail to behave as a one-component system?
6.18 Show that during a first order transition at constant pressure, entropy S of the entire system
varies linearly with the total volume V.
6.19 For the n -I transition in NH 4N0 3 , volume change ~ V and temperature of transition t vary
with pressure P as shown in table 6.D.

TABLE 6.D
P, atm 1 1000 2000 3000
t,OC 125.5 135.0 143.5 151.4
~V, cm 3 g'! 0.01351 0.01166 0.01020 0.00906

Calculate the heat of transition at 1,500 atm.
6.20 If the vapor pressure of CCl 4 is 25.83 atm at 240° C and 33.59 atm at 260° C and if its criti-
cal temperature is 283.2° C, what is its critical pressure?
6.21 The vapor pressure P of solid ammonia follows the equation

lnP = 23.03 _ 3754 K
T
while that of liquid ammonia follows the equation

lnP = 19.49 _ 3063 K.
T
Calculate (a) the temperature of the triple point and (b) the heat of fusion of ammonia
6.22 If a nonvolatile hydrocarbon added to benzene lowered its vapor pressure from 74.66 to
73.89 torr at 20° C, what was the activity of benzene in the solution?
6.23 What is the vapor pressure above a salt solution in which the mole-fraction activity of water
is 0.9325, at 25° C, where the vapor pressure of pure water is 23.76 torr?
6.24 For a solution of 3.795 g sulfur in 100.0 g CS 2 the boiling point was 46.66° C. For pure CS2
the boiling point is 46.30° C and the heat of vaporization 353.1 J g'! . What is the molecular
mass and the formula of sulfur in the CS 2?
6.25 If the osmotic pressure of an aqueous solution is 5.15 atm at 25° C, what is its freezing point?
6.26 Calculate the boiling point elevation when 1.000 g toluene is added to 100.0 g benzene.
Benzene boils at 80.1 ° C with a heat of vaporization of 30,765 J mol'! , while toluene has a
vapor pressure of 290.6 torr at 80.1 ° C with a heat of vaporization of 33,472 J mo}"!.
6.27 Solutions of iodoethane (B) in ethyl acetate (A) yielded partial pressures at 50° C as shown
in table 6.E. Obtain the Henry's law constants kA and kB by extrapolating P )XA and Pp)X B to
X A = 0 and to X B = O. Then calculate the activity of iodoethane (B) in the solutions on both
the Raoult's law and the Henry's law basis.
6.28 At a given temperature, the vapor pressure of solute is related to that of solvent by the equation
X A dPA + X B dPB =0.
PA PB