Calculating Masses of Reactants or Products from a Balanced Chemical Equation

To calculate the masses of reactants and products in a balanced chemical equation, it’s first important to know the molar masses of all elements or compounds involved. The molar mass can be determined using the periodic table, adding up the relative atomic masses of each element that makes up the compound.
The balanced equation ensures the law of conservation of mass is adhered to; the total mass of reactants equals the total mass of products formed.
Use the coefficient (number in front of a molecule) in the balanced chemical reaction to determine the ratio of molecules involved. This represents the number of moles of each reactant and product.
One mole of any substance will have a mass in grams equal to the relative molecular mass for that substance. For example, one mole of oxygen (O2) has a mass of 32g.
To calculate the mass of a certain reactant or product, multiply the number of moles by the molar mass.
You calculate the mass of product that can be made (the theoretical yield) from a certain amount of reactant. This can be used as a target for practical work.
If a question asks for the mass of a reactant needed to produce a certain mass of product, an understanding of mole ratios from the balanced equation is required.
Always ensure that your final answer makes sense within the context of the problem. For example, a mass of a reactant should not be more than the initial mass given.
In real life situations, the calculated mass of products is often not achieved due to factors such as impure reactants, incomplete reactions or other uncontrolled variables.
If the yield of a chemical reaction is provided, it can be used to calculate the practical yield. Theoretical yield multiplied by the percentage yield gives the practical (actual) yield. This can be further used to calculate masses in chemical reactions.