Coefficients in a chemical equation express between molecules or compounds.

Coefficients in a chemical equation express RATIOS between molecules or compounds.

In chemical equations, coefficient refers to those numerical numbers that are usually written at the front of elements' chemical symbols in order to balance the equations. Coefficients tell us the number of a particular element that must react with a specific number of another element in order for certain amount of chemical products to be produced; that is, it provide information about the reaction ratio of reactants and products. For instance, look at this chemical equation: N2 + 3H2 = 2NH3

In the equation given above, the coefficient of N2 is 1, the coefficient of H2 is 3 and the coefficient of NH3 is 2. What this equation is essentially telling us is that, in order to produce two molecules of ammonia, one molecule of nitrogen must react with three molecules of hydrogen. Thus, the equation gives the ratios between the product and the reactants.