A substance that undergoes a change in a chemical reaction is called a reactant or reagent. Usually, chemical reactions comprise of the changes that only pertain to the movement of electrons in the forming and breaking of chemical bonds.
In a chemical reaction, chemical substances undergo a chemical change yielding one or more products whose properties are different than those of reactants. Chemical reactions are depicted using chemical equations, which are graphical presentations of the reactants and the end products. These chemical equations consist of chemical formulas of the reactants and the products. Typically, the reactants are on the left side of the equation and the products on the right side.
Chemical reactions can either be exothermic or endothermic. Exothermic chemical reactions are reactions that require heat or energy for them to occur, whereas endothermic reactions release energy when they are completed.
Different chemical reactions are combined during chemical synthesis to produce a desired product. In biochemistry, similar combinations of chemical reactions form metabolic pathways. This same concept has been extended to reactions between entities smaller than atoms such as radioactive decays and nuclear reactions.
Types of chemical reactions include combustion, decomposition, synthesis, displacement and double displacement. In organic chemistry, chemical reactions that occur include oxidation, reduction and acid-base reactions.