| Noun | 1. | equilibrium constant - (chemistry) the ratio of concentrations when equilibrium is reached in a reversible reaction (when the rate of the forward reaction equals the rate of the reverse reaction) chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions constant - a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant" dissociation constant - the equilibrium constant for a reversible dissociation |