A chemical reaction is the process that occurs when two or more substances combine to produce a chemical change. The important terms to remember are:

Chemical Equation- name given to the shorthand used to describe the steps of a chemical reaction
Reactants- the starting materials for a chemical reaction; the substances that combine in the reaction
Products- the substances that are formed as a result of a chemical reaction
Chemical Reaction Rate- the speed at which a chemical reaction occurs
Activation Energy- the external energy that has to be added in order for a chemical reaction to occcur
Catalyst- a substance that helps a chemical reaction to occur (lowers the activation energy), but does not participate in the reaction itself
Law of Conservation of Mass- this Law states that matter is neither created nor destroyed in a chemical reaction. The number of reactant atoms of a chemical reaction will be the same as the number of product atoms.