equimolar

Equimolar describes a relation between quantities of substances expressed in moles. When two or more substances are equimolar, they contain the same number of moles, such that n1 = n2. This concept is commonly used to describe mixtures, reactants in a planned reaction, or systems where equal mole amounts are being compared. Equimolar does not imply equal masses or equal volumes, because different substances have different molar masses and densities.

In gas mixtures, equimolar means the components are present in equal numbers of moles. At a given temperature and pressure, equal moles of different gases occupy the same volume, so an equimolar gas mixture has equal volumes of each component under those conditions. In solutions or solids, equimolar usage typically refers to the comparison of amounts in moles rather than masses.

Examples help illustrate the idea. An equimolar mixture of hydrogen and oxygen might contain 1 mole of H2 and 1 mole of O2. For reactions, preparing equimolar amounts means setting the reactants so that nA = nB for the species involved; however, if the balanced equation has coefficients that are not equal, equimolar amounts may not meet the stoichiometric ratio, potentially making one reagent the limiting reactant.

Calculation often involves converting mass to moles using n = m/M, where m is mass and M is molar mass, to check whether components are present in equal mole quantities. Equimolar relationships are a basic tool in planning experiments, balancing reactions, and describing mixtures, but they must be interpreted in the context of the overall chemical equation and physical conditions.