Answer:
Substance at the beginning of a reaction- reactant
Substance at the end of a reaction- product
Number placed before a compound in a chemical equation- stoichiometric coefficient
Explanation:
In a reaction equation, the species written on the left hand side of the equation are called the reactants.
The reactants combine to form the species on the right hand side of the reaction equation called products.
The stoichiometric coefficient is a number written before the formula of a compound in the reaction equation.
