Dalton's Law of Partial Pressures
The total pressure of a gas mixture equals the sum of the pressures each component would exert alone in the same volume.
Formula / equation
p_total = p₁ + p₂ + p₃ …
Unit
Pa
In depth
Because ideal gas molecules do not interact, each component behaves independently of the others. The law lets gas mixtures be handled component by component and is essential in correcting for water vapour when a gas is collected over water.
Examples in the real world
Dry air at 101.3 kPa is roughly 79 kPa nitrogen plus 21 kPa oxygen; a diver's trimix is blended by partial pressure.