Editing Stoichiometry (section)

== Molar proportion ==
Stoichiometry is often used to balance chemical equations (reaction stoichiometry). For example, the two [[Diatomic molecule|diatomic]] gases, [[hydrogen]] and [[oxygen]], can combine to form a liquid, water, in an [[exothermic reaction]], as described by the following equation:
: {{chem2|2 H2 + O2 -> 2 H2O}}

Reaction stoichiometry describes the 2:1:2 ratio of hydrogen, oxygen, and water molecules in the above equation.

The molar ratio allows for conversion between moles of one substance and moles of another. For example, in the reaction
: {{chem2|2 CH3OH + 3 O2 -> 2 CO2 + 4 H2O}}

the amount of water that will be produced by the combustion of 0.27 moles of {{chem|CH|3|OH}} is obtained using the molar ratio between {{chem|CH|3|OH}} and {{chem|H|2|O}} of 2 to 4.
: <math>\left(\frac{0.27 \mbox{ mol }\mathrm{CH_3OH}}{1}\right)\left(\frac{4 \mbox{ mol }\mathrm{H_2O}}{2 \mbox{ mol } \mathrm{CH_3OH}}\right) = 0.54\ \text{mol }\mathrm{H_2O}</math>

The term stoichiometry is also often used for the [[Mole (unit)|molar]] proportions of elements in stoichiometric compounds (composition stoichiometry). For example, the stoichiometry of hydrogen and oxygen in {{chem|H|2|O}} is 2:1. In stoichiometric compounds, the molar proportions are whole numbers.