Chapter 12 Assignment Answers
18. Particles are closer together in solids than in liquids because of intermolecular
attractions.
23. Because the adhesive forces between water molecules and the silicon dioxide in
glass are greater than the cohesive forces between water molecules, the water rises
along the inner walls of the cylinder.
24. The cohesion between mercury atoms is stronger than the adhesion between
mercury and glass.
27. The addition of energy increases the kinetic energy of the particles, which reduces
the intermolecular forces between the particles. As energy is removed, the kinetic
energy of the particles decreases and intermolecular forces increase.
28. Freezing occurs when a liquid becomes a solid and energy is released. Melting
requires an input of energy to convert a solid to a liquid.
29. A substance undergoes deposition when it goes from the vapor phase to the solid
phase without going through the liquid phase. A substance undergoes sublimation
when it goes from the solid phase directly to the vapor phase without going through the
liquid phase.
30. In both processes, the substances become a vapor. During sublimation, the
substance goes from the solid phase directly to the vapor phase. During evaporation,
particles in a liquid gain enough energy to enter the vapor phase.
31. The combinations of temperature and pressure under which a given substance
exists as a solid, liquid and/or gas.
32. Triple point: the temperature at which the three phases of a substance can
coexist; critical point: the pressure and temperature above which a substance cannot
exist as a liquid.
33. liquid
34. the one in which no KE is lost.
35. It is directly proportional to their temperature.
38. Gases have low density, can be compressed, will expand to fill all available space,
and can undergo diffusion & effusion.
51. A temporary dipole forms when one molecule is close to another molecule, and the
electrons repel each other creating a greater electron density in one part of the
molecule. Permanent dipoles are found in polar molecules in which some regions of the
molecule are always partially positive & partially negative.
53. A hydrogen bond involves a large difference in electronegativity between the
hydrogen atom and the atom it is attached to (O, N, or F), making the bond extremely
polar.
63. Capillary action results from the opposing forces of adhesion & cohesion. Adhesive
forces between water molecules & the molecules in the glass of the capillary tube are
stronger than the cohesive forces holding water molecules together, so water moves up
the walls of the capillary tube.
68. Stronger intermolecular forces result in higher viscosity because the forces hold the
particles together too tightly for them to flow easily.
69. Surface tension increases with strength of interparticle forces. Water molecules
are held together by strong hydrogen bonds, resulting in higher surface tension; the
weaker dispersion forces between benzene molecules result in lower surface tension.
77. The temperature at which the crystal lattice of a solid disintegrates and it becomes
a liquid.
78. Boiling point is the temperature at which vapor pressure, exerted by liquid
molecules escaping from the surface of a sample, equals the atmospheric pressure
on the surface of the liquid.
79. Then water vapor in the air comes in contact with a cool object, it condenses on
the object.
82. Melting does not require as much energy because the particles in a solid do not
have to move far apart or gain much movement to form a liquid.
90. a. 100 o C
b. 78.5 o C
c. 94 o C