Key Terms – Chapter 05

Absolute zero The zero point on the absolute temperature scale; + 273.15°C or 0 K; theoretically, the temperature at which molecular motion is a minimum.

Atmosphere (atm) A unit of pressure; the pressure that will support a column of mercury 760 mm high at 0°C; 760 torr.

Avogadro’s Law At the same temperature and pressure, equal volumes of all gases contain the same number of molecules.

Barometer A device for measuring atmospheric pressure. See Figures 12-1 and 12-2. The liquid is usually mercury.

Boyle’s Law At constant temperature, the volume occupied by a given mass of a gas is inversely proportional to the applied pressure.

Charles’s Law At constant pressure, the volume occupied by a definite mass of a gas is directly proportional to its absolute temperature.

Condensed states The solid and liquid states.

Dalton’s Law of Partial Pressures The total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases.

Diffusion The movement of a substance (e.g., a gas) into a space or the mixing of one substance (e.g., a gas) with another.

Dispersion Forces Weak, short-range attractive forces between short-lived temporary dipoles.

Effusion The escape of a gas through a tiny hole or a thin porous wall.

Equation of state An equation that describes the behavior of matter in a given state; for example, the van der Waals equation describes the behavior of the gaseous state.

Fluids Substances that flow freely; gases and liquids.

Gay-Lussac’s Law of Combining Volumes At constant temperature and pressure, the volumes of reacting gases (and any gaseous products) can be expressed as ratios of small whole numbers.

Ideal gas A hypothetical gas that obeys exactly all postulates of the kinetic–molecular theory.

Ideal Gas Equation The product of the pressure and volume of an ideal gas is directly proportional to the number of moles of the gas and the absolute temperature.

Kinetic–molecular theory A theory that attempts to explain macroscopic observations on gases in microscopic or molecular terms.

Manometer A two-armed barometer. See Figure 12-1.

Mole fraction The number of moles of a component of a mixture divided by the total number of moles in the mixture.

Partial pressure The pressure exerted by one gas in a mixture of gases.

Pascal (Pa) The SI unit of pressure; it is defined as the pressure exerted by a force of one newton acting on an area of one square meter.

Pressure Force per unit area.

Real gases Gases that deviate from ideal gas behavior.

Root-mean-square speed, urmsThe square root of the mean-square speed, . This is equal to for an ideal gas. The root-mean-square speed is slightly different from the average speed, but the two quantities are proportional.

Standard molar volume The volume occupied by one mole of an ideal gas under standard conditions; 22.414 liters.

Standard temperature and pressure (STP) Standard temperature 0°C (273.15 K), and standard pressure, one atmosphere, are standard conditions for gases.

Torr A unit of pressure; the pressure that will support a column of mercury 1 mm high at 0°C.

Universal gas constant R, the proportionality constant in the ideal gas equation, PV = nRT.

van der Waals equation An equation of state that extends the ideal gas law to real gases by inclusion of two empirically determined parameters, which are different for different gases.

Vapor A gas formed by boiling or evaporation of a liquid or sublimation of a solid; a term commonly used when some of the liquid or solid remains in contact with the gas.

Vapor pressure The pressure exerted by a vapor in equilibrium with its liquid or solid.