Answers and Explanations
REVIEW QUESTIONS
1 . D
Because gas molecules have the greatest freedom to move around, gases have the greatest
disorder. Liquids are denser than gases and therefore the molecules experience stronger
intermolecular attractions and are less free to move around. The arrangement of molecules in
solids is the least random. Thus, melting and boiling are accompanied by an increase in
entropy, i.e., ∆S > 0. (See chapter 11 .)
2 . B
The miscibility of two liquids strongly depends on their polarities. In general, polar and
nonpolar liquids are not miscible, while a polar liquid can usually be mixed with another polar
liquid, and a nonpolar liquid with another nonpolar liquid. Choice A, molecular size, and
choice C, the density of a liquid, do not directly affect the miscibility (although choice C should
remind you that two immiscible liquids will form separate layers, with the denser liquid on the
bottom). Thus, B is the only correct choice.
3 . Ionic crystals contain repeating units of cations and anions. Because of the strong electrostatic
attraction between the ions, these crystals have high melting points. Since the charges in
these crystals are tightly fixed in the lattice, ionic solids are poor conductors of electricity. In
the liquid or solution phase the charged particles can move around, and thus liquid ionic
compounds will conduct electricity, as do solutions of such salts.
4 . B
The bonds between different metal atoms in an alloy are much weaker than those between
the atoms in pure metals. Therefore, breaking these bonds requires less energy than does
breaking the bonds in pure metals. Since melting and freezing points increase as the stability
of bonds increases, they tend to be lower for alloys than for pure metals.
