The law of conservation of mass states that matter is neither created nor destroyed. The mass of the reactants is therefore equal to the mass of the products. Solving problems involving the law of conservation of mass is a main concept used for comprehending chemical equations. Predictions about the mass of a reactant or a product can be determined by knowing the masses of the other reactants and products.
Write out the chemical reaction. Law of conservation of mass problems usually provide information about the composition of reactants and products. For example, the problem may state that carbon reacts with oxygen to form carbon dioxide. The equation for this is C + O2 = CO2.
Write down the information that the problem provides about the masses of the reactants and products. For example, there may be 30.0 g of carbon and 40.0 g of carbon dioxide. The problem asks you to find the amount of oxygen.
Subtract the known amount of reactants from the total amount of the products. For example, if there are 40.0 g of product, then there should be a total of 40.0 g of reactants. By subtracting 30.0 g of carbon from 40.0 g of carbon dioxide, you can determine that there are 10.0 g of oxygen.
Check your answer by adding the amounts of the reactants. For example, adding the amounts of the carbon and oxygen, 30.0 g + 10.0 g = 40.0 g. Since you know there are 40.0 g of CO2, the product, you know the answer is correct.