Law of Definite Proportions
A given chemical compound always contains its component elements in the same fixed ratio by mass, regardless of source.
Formula
Variables
Example
Pure water is always 11.2% hydrogen and 88.8% oxygen by mass.
Did You Know?
Proposed by Joseph Proust around 1797, it was key evidence for Dalton's atomic theory.
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More in Scientific Laws & Principles
View allLaw of Conservation of Mass
BasicIn a closed system, matter is neither created nor destroyed — the total mass before a reaction equals the total mass after.
Law of Multiple Proportions
IntermediateWhen 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.
Dalton's Law of Partial Pressures
IntermediateThe total pressure of a mixture of non-reacting gases equals the sum of the partial pressures each gas would exert alone.
Graham's Law of Effusion
IntermediateThe rate at which a gas effuses through a tiny hole is inversely proportional to the square root of its molar mass.
Avogadro's Law
BasicAt the same temperature and pressure, equal volumes of gases contain equal numbers of molecules — so volume is proportional to moles.
Raoult's Law
AdvancedThe vapour pressure of a solvent above a solution equals its mole fraction times the pure solvent's vapour pressure.