Definitions for "Rate constant"
The proportionality constant in the equation that describes the relation-ship between the rate of a step in a chemical reaction and the product of the concentrations of the reactants consumed in that step.
A parameter that, when multiplied by the driving force, determines the rate of disappearance of the reactants. The rate constant is a function of temperature and (sometimes) pressure. The functional form is usually modified Arrhenius (k = A T^n exp(-Ea/RT)), however more complicated expressions are used for pressure-dependent reactions (see www.ReactionXML.org for details). The driving force is typically the product of the reactant concentrations raised to the power of their stoichiometric coefficients.
Of a particular chemical reaction, a constant which, when multiplied by the concentration(s) of reactant(s), gives the rate of the reaction.