Key Words 483
critical point The temperature and pressure at which
the physical properties of the liquid phase and vapor
phase of a substance become indistinguishable.
(p. 460)
critical pressure The highest pressure at which a liquid
and gas coexist in equilibrium. (p. 460)
critical temperature The highest temperature at which a
liquid and a gas coexist in equilibrium. (p. 460)
deposition The process of a gas undergoing a phase
transition to a solid; the opposite of sublimation.
(p. 452)
dynamic equilibrium A term sometimes used in chem-
istry as synonymous with equilibrium to emphasize
that molecular-level equilibrium is not static.
(p. 453)
equilibrium In a reaction or process, a condition
wherein the rates of the forward and backward reac-
tions are equal. The amounts of the reactants and
products do not change, but the forward and back-
ward reactions are still proceeding. (p. 453)
equilibrium vapor pressure The pressure exerted by the
vapor of a liquid or solid under equilibrium condi-
tions. (p. 453)
evaporation The process of a liquid undergoing a
phase transition to a gas; the opposite of condensa-
tion. (p. 452)
freezing-point depression The lowering of the melting
point of a compound due to the presence of a dis-
solved solute. (p. 478)
gas The phase of a substance characterized by widely
spaced components exhibiting low density, ease of
flow, and the ability to occupy an enclosed space in
its entirety. (p. 443)
heat of fusion (∆
fus
H) The enthalpy change associated
with the phase transition from liquid to solid.
(p. 457)
heat of solution (∆
sol
H) The enthalpy change associated
with the dissolution of a solute into a solvent.
(p. 466)
heat of vaporization (∆
vap
H) The enthalpy change asso-
ciated with the phase transition from a liquid to a
gas. (p. 457)
heating curve A plot of the temperature of a com-
pound versus time or energy as heat is added at
constant pressure. The plot indicates the specific
temperature ranges for solid, liquid, and gas phases.
(p. 456)
Henry’s law The solubility of a gas is directly propor-
tional to the pressure that the gas exerts above the
solution. (p. 472)
hydration The interaction of water (as the solvent)
with dissolved ions. (p. 466)
hydrogen bond A particularly strong intermolecular
force of attraction between F, O, and/or N and a
hydrogen atom. (p. 448)
hypertonic Containing a concentration of ions greater
than that to which it is judged against. (p. 480)
hypotonic Containing a concentration of ions lower
than that to which it is judged against. (p. 480)
ideal solution A solution in which the properties of the
solute and solvent are not changed by dilution. This
means that other than being diluted, combining
solute and solvent in an ideal solution does not
release or absorb heat, and the total volume in the
solution is the sum of the volumes of the solute and
solvent. (p. 474)
induced dipole A dipole produced in a compound as a
consequence of its interaction with an adjacent
dipole. (p. 446)
intermolecular force A force of attraction between two
molecules. (p. 444)
ion–dipole interaction An attraction between an ion and
a compound with a dipole. (p. 466)
isotonic Containing the same concentration of ions.
(p. 480)
isosmotic Possessing the same osmotic pressure.
(p. 480)
liquid A phase of a substance characterized by closely
held components. The properties of a liquid include
a medium density, the ability to flow, and the ability
to take the shape of the container that holds it by
filling from the bottom up. (p. 443)
London forces The weakest of the intermolecular forces
of attraction, characterized by the interaction of
induced dipoles. (p. 446)
maximum contaminant level (MCL) The highest acceptable
level of a contaminant in a particular solution, ac-
cording to the Environmental Protection Agency.
(p. 470)
melting point The temperature of the phase transition
as a compound changes from a solid to liquid.
(p. 456)
meniscus The concave or convex shape assumed by the
surface of a liquid as it interacts with its container.
(p. 464)
miscible Mixable. Two solvents that are miscible dis-
solve in each other completely. (p. 466)
molality A concentration measure defined as moles of
solute per kilogram of solvent. (p. 468)
molarity A concentration measure defined as moles of
solute per liter of solution. (p. 468)
mole fraction A concentration measure defined as
moles of solute per total moles of solution. (p. 468)
natural gas A complex mixture of gases extracted from
the Earth. The major component in many cases is
methane. (p. 443)
normal boiling point The temperature at which a liquid
boils when the pressure is 1 atm. (p. 455)
osmosis The flow of solvent into a solution through a
semipermeable membrane. (p. 479)