## ::Partial pressure

### ::concepts

Align::pressure    Partial::right    Mixture::mathrm    Total::volume    Henry's::gases    Absolute::oxygen

In a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> The total pressure of an ideal gas mixture is the sum of the partial pressures of each individual gas in the mixture.

It relies on the following isotherm relation:

$\frac{V_x}{V_{tot}} = \frac{p_x}{p_{tot}} = \frac{n_x}{n_{tot}}$
• Vx is the partial volume of any individual gas component (X)
• Vtot is the total volume in gas mixture
• px is the partial pressure of gas X
• ptot is the total pressure of gas mixture
• nx is the amount of substance of a gas (X)
• ntot is the total amount of substance in gas mixture

The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases dissolve, diffuse, and react according to their partial pressures, and not according to their concentrations in gas mixtures or liquids.

This general property of gases is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood.

Partial pressure sections
Intro  Dalton's law of partial pressures  Ideal gas mixtures  Partial volume (Amagat's law of additive volume)  Vapor pressure  Equilibrium constants of reactions involving gas mixtures  Henry's Law and the solubility of gases  Partial pressure in diving breathing gases  In medicine  See also  References

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