Now you can see that being able to write a balanced equation is really a very good shorthand way of describing what happens in a chemical reaction. When a chemical reaction occurs, it can be described by an equation. The reactants are the substances that you start with and are written on the left side of an arrow. If there are two or more reactants, they are separated by a plus sign. The products are written on the right side of the arrow and those are the substances that you end up with. All substances are written using the correct formula. The equation is also balanced using coefficients in order to obey the Law of Conservation of Mass, which says that matter cannot be created or destroyed. The coefficients indicate the number of moles or molecules of each substance. A balanced equation may also have phase notation, which indicates whether a substance is a solid, liquid, or gas.