The answer is: The starting materials in a chemical reaction are called reactants... or can be called reagents too.
The principal component in a chemical reaction are the reactants, after the reaction, we have the products and we could have reactants too (if they are not completed consumed).
For example, given the following reaction:
[tex]2C2H6+7O2 = 4CO2 + 6H2O[/tex]
Reactants are: 2C2H6 and 7O2
Products are: 4CO2 and 6H2O
Have a nice day!