- absolute zero
- temperature at which the volume of a gas would be zero according to Charles’s law.

- Amontons’s law
- (also, Gay-Lussac’s law) pressure of a given number of moles of gas is directly proportional to its kelvin temperature when the volume is held constant

- atmosphere (atm)
- unit of pressure; 1 atm = 101,325 Pa

- Avogadro’s law
- volume of a gas at constant temperature and pressure is proportional to the number of gas molecules

- bar
- (bar or b) unit of pressure; 1 bar = 100,000 Pa

- barometer
- device used to measure atmospheric pressure

- Boyle’s law
- volume of a given number of moles of gas held at constant temperature is inversely proportional to the pressure under which it is measured

- Charles’s law
- volume of a given number of moles of gas is directly proportional to its kelvin temperature when the pressure is held constant

- compressibility factor (Z)
- ratio of the experimentally measured molar volume for a gas to its molar volume as computed from the ideal gas equation

- Dalton’s law of partial pressures
- total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the component gases.

- diffusion
- movement of an atom or molecule from a region of relatively high concentration to one of relatively low concentration (discussed in this chapter with regard to gaseous species, but applicable to species in any phase)

- effusion
- transfer of gaseous atoms or molecules from a container to a vacuum through very small openings

- Graham’s law of effusion
- rates of diffusion and effusion of gases are inversely proportional to the square roots of their molecular masses

- hydrostatic pressure
- pressure exerted by a fluid due to gravity

- ideal gas
- hypothetical gas whose physical properties are perfectly described by the gas laws

- ideal gas constant (
*R*) - constant derived from the ideal gas equation
*R*= 0.08206 L atm mol^{–1}K^{–1}or 8.314 L kPa mol^{–1}K^{–1}

- ideal gas law
- relation between the pressure, volume, amount, and temperature of a gas under conditions derived by combination of the simple gas laws

- kinetic molecular theory
- theory based on simple principles and assumptions that effectively explains ideal gas behavior

- manometer
- device used to measure the pressure of a gas trapped in a container

- mean free path
- average distance a molecule travels between collisions

- mole fraction (
*X*) - concentration unit defined as the ratio of the molar amount of a mixture component to the total number of moles of all mixture components

- partial pressure
- pressure exerted by an individual gas in a mixture

- pascal (Pa)
- SI unit of pressure; 1 Pa = 1 N/m
^{2}

- pounds per square inch (psi)
- unit of pressure common in the US

- pressure
- force exerted per unit area

- rate of diffusion
- amount of gas diffusing through a given area over a given time

- root mean square velocity (
*u*_{rms}) - measure of average velocity for a group of particles calculated as the square root of the average squared velocity

- standard conditions of temperature and pressure (STP)
- 273.15 K (0 °C) and 1 atm (101.325 kPa)

- standard molar volume
- volume of 1 mole of gas at STP, approximately 22.4 L for gases behaving ideally

- torr
- unit of pressure; $\text{1 torr}=\phantom{\rule{0.2em}{0ex}}\frac{1}{760}\phantom{\rule{0.2em}{0ex}}\text{atm}$

- van der Waals equation
- modified version of the ideal gas equation containing additional terms to account for non-ideal gas behavior

- vapor pressure of water
- pressure exerted by water vapor in equilibrium with liquid water in a closed container at a specific temperature