A reactant in a chemical equation is a substance that starts or takes part in a chemical reaction.
Key points about reactants:
- They are the starting materials of a reaction.
- They are written on the left side of the chemical equation.
- During the reaction, their atoms are rearranged to form new substances (the products).
- Reactants are consumed or changed as the reaction proceeds, but the total number of atoms is conserved (law of conservation of mass).
For example, in the reaction of hydrogen with oxygen to form water, hydrogen and oxygen are the reactants.
In simple words:
Reactants go in to a reaction, and products come out of it.