Chemical equations represent chemical reactions.
Part of the problem of writing equations is determining the products formed. We have no sure method of predicting products, nor do we have time to carry out experimentally all the reactions we may wish to consider. Therefore, we must use data reported in the writings of other workers, certain rules to aid in our predictions, and the atomic structure and combining capacities of the elements to help us predict the formulas of the products of a chemical reaction. The final proof of the existence of any reaction, of course, is the actual observation of the reaction in the laboratory. Reactions are classified into types to assist in writing equations and to aid in predicting other reactions.