Stoichiometry

Chemists often need to measure the quantities of elements and compounds reacting. Stoichiometry means measuring elements. Atoms of different elements (and sometimes the same element too) have different masses, so we need to take that into account when calculating reacting masses. The 'big numbers' that we put in front of formulae in chemical equations are the stoichiometric coefficients. Stoichiometry involves the concept of the mole.