Chemical Reaction

A chemical reaction is when there is a change in the molecular make up of a material. This can happen when two substances are combined to create a new substance.Chemical reaction rates can be increased or decreased by various factors such as concentration, temperature, surface area, and catalysts or inhibitors. The four types of chemical reactions that can occur are synthesis, decomposition, replacement, and ionic. Chemical reactions are also chemical change.
A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.
Physical changes can be reversed, chemical changes cannot be reversed with the substance changed back without extraordinary means.