in chemistry, the proportion of an element which will combine with or replace unit weight of hydrogen. When multiplied by the valency it gives the atomic weight. The determination of equivalent weights is treated in the article Stoichiometry. (See also Chemistry.) In a more general sense the term "equivalent" is used to denote quantities of substances which neutralize one another, as for example NaOH, HCI, 1H 2 SO 4, 2Ba(OH)2.