Key Gas Law Equations to Know for AP Physics 2 (2025)

Ideal Gas Law

Describes the relationship between pressure, volume, temperature, and the amount of gas, assuming ideal conditions.

Boyle's Law

States that pressure and volume are inversely proportional at constant temperature.

Charles's Law

States that volume and temperature are directly proportional at constant pressure.

Gay-Lussac's Law

States that pressure and temperature are directly proportional at constant volume.

Combined Gas Law

Combines Boyle’s, Charles’s, and Gay-Lussac’s laws for situations where pressure, volume, and temperature change, but moles remain constant.

Avogadro's Law

States that the volume of a gas is directly proportional to the number of moles at constant temperature and pressure.

Dalton's Law of Partial Pressures

States that the total pressure of a gas mixture equals the sum of the partial pressures of each gas.

Kinetic Theory of Gases

Explains gas behavior by relating pressure and volume to the microscopic behavior of gas particles.

Root Mean Square Speed

Calculates the average speed of gas molecules based on temperature and molar mass.

Molar Mass from Density

Relates gas density to molar mass, temperature, and pressure.

R (Universal Gas Constant)

A constant used in the Ideal Gas Law, value of 8.31 J/(mol·K) or 0.0821 L·atm/(mol·K).

Pressure (P)

The force exerted by gas molecules per unit area.

Volume (V)

The space occupied by gas, generally measured in liters or m³.

Temperature (T)

A measure of the average kinetic energy of gas particles, must be in Kelvin.

Moles (n)

A measure of the amount of substance, indicating the number of gas particles.

Elastic Collisions

Collisions between gas molecules and container walls where no kinetic energy is lost.

Average Kinetic Energy

The energy associated with the motion of gas particles, proportional to temperature.

Inversely Proportional

A relationship where an increase in one variable results in a decrease in another.

Directly Proportional

A relationship where an increase in one variable results in an increase in another.

Ideal Gas

A hypothetical gas that perfectly follows the gas laws with no intermolecular forces.

Graham's Law

Describes the rate of diffusion and effusion of gases, stating lighter gases diffuse faster.