A balanced chemical equation allows a person to determine the molar ratios of reactants needed to carry out the equation to completion. A molar ratio takes into account the molecular weight of a substance when attempting to ascertain how much of a chemical is needed. Molar ratios are expressed as coefficients to the left of the reactants and products.
For example, the chemical equation N2 + 3H2 --> 2NH3 is one mole of nitrogen molecules plus three moles of hydrogen molecules that create two moles of ammonia. The equation is balanced because the same number of moles of nitrogen and hydrogen are on both sides of the equation. There are two moles of nitrogen gas and six moles of hydrogen gas as reactants and products.
A mole is a chemical ratio that describes the weight of a substance based on the size of its atoms and molecules. One mole of a substance is 6.022 x 10^23 molecules or atoms. One mole of ammonia weighs about 17 grams, whereas six moles of hydrogen is 6 grams. Yet one mole of both substances is the same amount of individually discernible parts.
The atomic mass of elements is listed above each element on the Periodic Table of Elements. Hydrogen is the lightest element where one mole is 1 gram.