Partial pressure is the pressure exerted by a single gas in a mixture of gases. The concept of partial pressure is based on the ideal gas law, which assumes that the gases in the mixture do not interact with each other and that they behave as ideal gases. The ideal gas law relates the partial pressure of a gas to its temperature, volume, and the number of moles of gas.

Partial pressure is an important concept in gas chemistry and is used in various applications, such as in the calculation of the equilibrium constant of a gas reaction, in the measurement of the composition of gas mixtures, and in the determination of the oxygen content in breathing air.