Reactants: definition in chemistry
Reactants: The starting substances in a chemical reaction, written on the left side of a chemical equation.
During a reaction, bonds in the reactants break and the atoms rearrange to form products. Atoms are neither created nor destroyed, so a balanced equation has the same number of each kind of atom on both sides. The reactant that runs out first is called the limiting reactant, because it limits how much product can form.
Examples
- In 2H₂ + O₂ → 2H₂O, hydrogen and oxygen are the reactants
- Wood and oxygen are the reactants when a campfire burns
- Baking soda and vinegar are the reactants in a fizzing volcano
- Carbon dioxide and water are the reactants in photosynthesis
On the periodic table
An element's position helps predict how it reacts: for example, alkali metals in group 1 react readily with halogens in group 17.