Scientific Laws & Principles

Intermediate

Dalton's Law of Partial Pressures

The total pressure of a mixture of non-reacting gases equals the sum of the partial pressures each gas would exert alone.

Formula

P_{\text{total}} = P_1 + P_2 + \cdots + P_n

Variables

P_{\text{total}}Total pressure

P_iPartial pressure of gas i

Example

Dry air ≈ 0.78 atm N₂ + 0.21 atm O₂ + 0.01 atm other ≈ 1 atm.

Did You Know?

This is why divers must track partial pressures — oxygen becomes toxic at high partial pressure even though the fraction is unchanged.

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More in Scientific Laws & Principles

Law of Conservation of Mass

In a closed system, matter is neither created nor destroyed — the total mass before a reaction equals the total mass after.

Law of Definite Proportions

A given chemical compound always contains its component elements in the same fixed ratio by mass, regardless of source.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element combining with a fixed mass of the other are in ratios of small whole numbers.

Graham's Law of Effusion

The rate at which a gas effuses through a tiny hole is inversely proportional to the square root of its molar mass.

Avogadro's Law

At the same temperature and pressure, equal volumes of gases contain equal numbers of molecules — so volume is proportional to moles.

Raoult's Law

The vapour pressure of a solvent above a solution equals its mole fraction times the pure solvent's vapour pressure.