In chemistry and physics, Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.[1] This empirical law was observed by John Dalton in 1801 and published in 1802.[2] Dalton's law is related to the ideal gas laws.


Mathematically, the pressure of a mixture of non-reactive gases can be defined as the summation:

\( {\displaystyle p_{\text{total}}=\sum _{i=1}^{n}p_{i}} \) or \( {\displaystyle p_{\text{total}}=p_{1}+p_{2}+p_{3}+\cdots +p_{n}} \)

where p1, p2, ..., pn represent the partial pressures of each component.[1]

\( {\displaystyle p_{i}=p_{\text{total}}x_{i}} \)

where xi is the mole fraction of the ith component in the total mixture of n components.
Volume-based concentration

The relationship below provides a way to determine the volume-based concentration of any individual gaseous component

\( {\displaystyle p_{i}=p_{\text{total}}c_{i}} \)

where ci is the concentration of component i .

Dalton's law is not strictly followed by real gases, with the deviation increasing with pressure. Under such conditions the volume occupied by the molecules becomes significant compared to the free space between them. In particular, the short average distances between molecules increases intermolecular forces between gas molecules enough to substantially change the pressure exerted by them, an effect not included in the ideal gas model.
See also

Amagat's law – Gas law describing volume of a gas mixture
Boyle's law – Relationship between pressure and volume in a gas at constant temperature
Combined gas law – Combination of Charles', Boyle's and Gay-Lussac's gas laws
Gay-Lussac's law – Relationship between pressure and temperature of a gas at constant volume.
Henry's law – Relation of equilibrium solubility of a gas in a liquid to its partial pressure in the contacting gas phase
Mole (unit) – SI unit of amount of substance
Partial pressure – Pressure attributed to a component gas in a mixture
Raoult's law – A law of thermodynamics for vapour pressure of a mixture
Vapor pressure


Silberberg, Martin S. (2009). Chemistry: the molecular nature of matter and change (5th ed.). Boston: McGraw-Hill. p. 206. ISBN 9780073048598.
J. Dalton (1802), "Essay IV. On the expansion of elastic fluids by heat," Memoirs of the Literary and Philosophical Society of Manchester, vol. 5, pt. 2, pages 595–602; see page 600.

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