16. When electricity is passed through water, the following decomposition reaction can occur: 2H2O → 2H +02 What does the law of conservation of matter tell you about the ratios of particles in the chemical reaction? A The reacting substances must be the same as the substances produced. 8. The number of reactant molecules must equal the number of product molecules. The number of reactant compounds must equal the number of product compounds. D. The number of atoms of each element must be equal on both sides of the reaction arrow.