chemical equivalence

In chemistry, "chemical equivalence" refers to the concept of equivalent weight. This is the quantity of a substance that exactly reacts with a fixed quantity of another substance in a specific chemical reaction. While the concept of equivalent weight has largely been replaced by molar mass, it was historically used to describe how substances combine in precise, or chemically equivalent, proportions. For elements, equivalent weight is calculated by dividing the atomic weight by the valence, or combining power. For compounds acting as oxidizing or reducing agents, it's the molecular weight divided by the number of electrons lost or gained per molecule. For acids and bases, it relates to the amount that furnishes or reacts with a specific amount of hydrogen or hydroxide ions.1