# Gases

## Vocabulary

### absolute temperature

temperature as compared to absolute zero, the cessation of all motion, even subatomic motion, measured in kelvins (K)

### atmosphere (atm)

unit of pressure (force per unit area) equal to 760 mm Hg. The average atmospheric pressure at sea level is defined as 1 atmosphere.

law that states that equal volumes of gases at the same temperature and pressure have equal numbers of atoms or molecules, represented by the equation $\frac{V_1}{n_1}=\frac{V_2}{n_2}$

### bar

unit of pressure equal to 100,000 Pa

### barometer

open tube filled with liquid such as mercury and sealed at the other end under a vacuum, used to measure atmospheric pressure (of gas, in mm Hg)

### Boyle's law

law that states that pressure of gas increases as volume decreases at constant temperature and moles of gas, represented by the equation $P_1V_1=P_2V_2$

### Charles's law

law that states that the volume of gas increases as temperature increases at constant pressure and moles of gas, represented by the equation $\frac{V_1}{T_1}=\frac{V_2}{T_2}$

### compressibility factor (Z)

describes how much a gas's behavior differs from ideal

### Dalton's law of partial pressures

law that states that the total pressure of a mixture of ideal and nonreacting gases is the sum of the partial pressures of the individual gases

### diffusion

process by which gas moves from an area of higher concentration to an area of lower concentration

### effusion

process by which gases move through small openings in solids, one particle at a time

### gas

state of matter that has neither a definite volume nor a definite shape, consisting of particles that are far apart and move randomly to fill their container

### Gay-Lussac's law

law that states that for an ideal gas with constant mass and volume, the pressure exerted on the container is proportional to its absolute temperature, represented by the equation $\frac{P_1}{T_1}=\frac{P_2}{T_2}$

### Graham's law

law that states that the rate of effusion of a gas is inversely proportional to the square root of its mass, represented by the equation $\frac{{\rm{rate}}_1}{{\rm{rate}}_2}=\sqrt{\frac{M_2}{M_1}}$

### Henry's law

law that states that the amount of a gas that dissolves in a certain type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid at a specific temperature, represented by the equation $C=kP_{\rm{gas}}$

### ideal gas

theoretical gas in which no forces are acting on the gas particles, and the particles do not take up space

### ideal gas law

law that describes the behavior of ideal gases, represented by the equation $PV=nRT$

### kinetic molecular theory

theory involving the relationship between temperature, pressure, and volume that states that the average kinetic energy of a gas is proportional to its temperature

### manometer

instrument that measures gas pressure (in mm Hg) via a tube of liquid that is open at both ends

### mean free path

average distance that a gas particle travels before colliding with another gas particle

### mole fraction

concentration expressed as the moles of solvent divided by the total number of all moles in a solution

### partial pressure

pressure of an ideal gas that contributes to the total pressure of a mixture of gases at constant temperature

### pascal (Pa)

SI unit of gas pressure

### pounds per square inch (psi)

unit that describes the pounds of force applied to a square inch (area) of a container

### pressure

force applied perpendicular to a unit area of surface

### standard molar volume

volume occupied by one mole of an ideal gas at STP (standard temperature and pressure), equal to 22.4 L

### standard temperature and pressure (STP)

1 atmosphere (atm) pressure and 0°C (273.15 K) temperature

### torr

absolute unit of pressure, defined as 1/760 atmosphere (atm)

### van der Waals equation

equation that accounts for intermolecular (nonideal) interactions between gases. It adjusts the ideal gas law to explain and predict the behavior of real gases.