Substances on the left side of a chemical equation are called reactants. Substances that are found on the right side are referred to as products. In a chemical reaction, the reactants are used up and converted into products.
A chemical reaction occurs when substances with inherent chemical properties and definite compositions react with each other to create new substances that are characteristically different from the original substances. These substances can either be in the form of an atom, which is the fundamental unit of a chemical element, or a molecule, which is the smallest unit of a chemical compound. One way of illustrating the relationship between the substances that are in involved in a chemical reaction is through a chemical equation.
All the molecular formulas of the atoms or molecules on the left portion of the equation are added to create the atoms or molecules that are also added on the right side of the equation. Chemical equations often specify the state of matter of the substances present in a chemical reaction by enclosing the symbol in parenthesis: (s) for solids, (l) for liquids, (g) for gases and (aq) for aqueous solutions. Numeral coefficients are also used to ensure that the number of atoms in the reactants is equivalent to the number of atoms in the products. Chemical reactions can be of several types, which include double-replacement reactions, neutralization reactions, redox reactions, combustion reactions, synthesis reactions or decomposition reactions.