In a chemical reaction, the reactants are the elements present when the reaction begins, and the products are the elements and compounds produced as a result of the reaction. In a chemical formula, the reactants are on the left side of the arrow, and the products are on the right.
A chemical reaction results in the forming or breaking apart of chemical bonds between various elements. These reactions can result in many different outcomes, which can be affected by temperature, pressure and the amount of the reactants. Catalysts can also start a reaction or speed up its rate. However, the catalyst is not involved in the chemical reaction, as it remains unchanged before and after the reaction.
Although the elements and compounds may change form during the reaction, every atom in the reactants is also found in one of the products. In the reaction, individual elements can bond together to form compounds, or compounds can break apart into elements. For instance, when water is exposed to an electrical current, it breaks apart into oxygen and hydrogen gases. Alternatively, when zinc and sulfur react together, the two elements bond together to form zinc sulfide.
Some reactions also result in chemical equilibrium, which occurs when the reactants change into products at the same time as the products change back into the original reactants.