What is the formula for measuring rate of a chemical reaction?

A chemical reaction involves the rearranging of atoms of the same or different elements to form new substances. It is represented by a chemical equation in which the reactants (substances that are broken apart) are written on the left and the products (new substances formed) are written on the right. If more than one reactant or product is needed, they are separated with a + sign. An arrow is used to separate the reactant side of the equation from the product side.