<Dl> <Dd> r = k (A) x (B) y (\ displaystyle r \; = \; k (\ mathrm (A)) ^ (x) (\ mathrm (B)) ^ (y)) </Dd> </Dl> <Dd> r = k (A) x (B) y (\ displaystyle r \; = \; k (\ mathrm (A)) ^ (x) (\ mathrm (B)) ^ (y)) </Dd> <P> where (A) and (B) express the concentration of the species A and B (usually in moles per liter (molarity, M)). The exponents x and y are the partial orders of reaction for A and B and the overall reaction order is the sum of the exponents . These are often positive integers, but they may also be zero, fractional, or negative . The constant k is the reaction rate constant or rate coefficient of the reaction and has units of 1 / time . Its value may depend on conditions such as temperature, ionic strength, surface area of an adsorbent, or light irradiation . </P> <P> Elementary (single - step) reactions have reaction orders equal to the stoichiometric coefficients for each reactant . The overall reaction order, i.e. the sum of stoichiometric coefficients of reactants, is always equal to the molecularity of the elementary reaction . Complex (multi-step) reactions may or may not have reaction orders equal to their stoichiometric coefficients . </P>

What is the k in the rate law equation