Chapter 12

1.) Which factor has an effect on the value of the normal boiling point of a liquid?

a. atmospheric pressure

b. rate of condensation

c. rate of evaporation

d. strength of the intermolecular forces

e. rate of temperature increase

2.) Benzene, C6H8, has an enthalpy of fusion of 127.4 J g-1 and its melting point temperature is

5.53 °C. How much heat is required to transform 80.0 g of solid benzene at 5.53 °C into liquid

benzene, also at 5.53 °C?

a. 705 J

b. 10.2 kJ

c. 14.4 kJ

d. 19.3 kJ

e. 22.3 kJ

3.) Find the boiling point temperature, °C, at 760 torr of an isomer of octane, C8H18, if its

enthalpy of vaporization is 38,210 J mol-1 and its vapor pressure at 110.0 °C is 638.43 torr.

a. 111.52 °C

b. 113.22 °C

c. 115.00 °C

d. 115.65 °C

e. 118.30 °C

4.) Hexane (C6H14) boils at 68.73 °C at 760 torr of pressure. The molar enthalpy of vaporization

for hexane is 28.9 kJ/mol. What would be the vapor pressure of hexane at 30 °C?

a. 207 torr

b. 546 torr

c. 2786 torr

d. 759 torr

e. 2396 torr

5.) The normal boiling point of 2,3,4-trimethypentane, C8H18, is 113.47 °C, and its molar

enthalpy of vaporization is 37,600 J mol-1. What is its vapor pressure, in torr, at 105.5 °C?

a. 479.7 torr

b. 586.6 torr

c. 594.1 torr

d. 616.2 torr

e. 694.4 torr

6.) Arrange these compounds in order of increasing intermolecular attractive forces: CCl4, GeCl4,

SiCl4, SnCl4.

________________________

Answer: CCl4 < SiCl4 < GeCl4 < SnCl4

7.) Evaporation

a. is an endothermic process.

b. is an exothermic process.

c. involves breaking intermolecular forces.

d. leads to lower temperatures on the surface where it occurs.

e. a, c, and d

8.)Substance A has a normal melting point of -25.0 °C, an enthalpy of fusion of 1200 J g-1;

specific heats for the solid and the liquid are 3.00 and 6.20 J g-1 °C -1, respectively. To change

150 grams of A from a solid at –40.0 °C to a liquid at +70.0 °C

a. will require 1.52 x 105 joules.

b. will require 1.81 x 105 joules.

c. will require 2.21 x 103 joules.

d. will require 2.29 x 105 joules.

e. will require 2.75 x 105 joules.

9.) If 22.4 g of a solid with a molecular weight of 148.0 g/mol, which is already at its melting point,

requires 5.358 kJ of heat to melt it, what is the molar enthalpy of fusion, in kJ mol-1?

a. 1.23 x 104 kJ mol-1

b. 0.811 kJ mol-1

c. 35.4 kJ mol-1

d. 0.0282 kJ mol-1

e. 1.78 x 104 kJ mol-1

10.) Which of the following is not a factor that directly affects the viscosity of a liquid?

a. size of the molecule

b. polarizability

c. boiling point

d. bulk, branching, or length of molecule

e. polarity

11.) It is thought that the strongest intermolecular forces between molecules of NO are

a. covalent bonds.

b. dipole-dipole interactions.

c. ionic bonds.

d. hydrogen bonds.

e. London forces.

12.) Which covalent compound will exhibit hydrogen bonding in the liquid state?

a. CH2F2

b. Cl2NH

c. H2PCl

d. HBr

e. NCl3

13.) The property that measures or describes the magnitude of resistance to flow in a liquid is called

a. London forces

b. malleability

c. surface tension

d. vapor pressure

e. viscosity

14.) At 1.0 atm pressure, ice (solid H2O) floats in water instead of sinking. The reason for this is

a. when water freezes, it expands instead of contracting.

b. the fusion process is endothermic, therefore the solid will float.

c. the triple point has a lower temperature than the freezing point for water.

d. the critical temperature has a higher temperature than the normal boiling point.

e. the triple point corresponds to a pressure below 1 standard atmosphere.

15.) A substance has a normal boiling point of +89.3 °C, an enthalpy of vaporization of 2600 J g-1;

specific heats for the liquid and the gas are 6.20 and 3.20 J g-1 °C -1, respectively. How much energy, in

joules, is needed to change 150 grams of the substance from a liquid at –10.0 °C to a gas at +129.0 °C?

Answer: 5.01 x 105 joules

16.) The molar enthalpy of vaporization of carbon disulfide is 26.74 kJ/mol, and its normal boiling point

is 46 °C. What is the vapor pressure of CS2 at 0°C in torr?

Answer: 139 torr

17.) Arrange the following compounds in order of increasing viscosity: methylene chloride

(CH2Cl2); glycerin (C3H5(OH)3); 1,1-ethandiol (C2H4(OH)2); and acetone (C3H6O). Explain your reasoning.

Answer: Methylene chloride < acetone < 1,1-ethanediol < glycerin. We rationalize the choice by

examining intermolecular forces. Methylene chloride is nearly nonpolar, while acetone will have dipole-

dipole attractions. Glycerin and 1,1-ethanediol, however, have H-bonding, with glycerin having the

most.