Definition: proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); in the reaction A ? B + C, the rate of the reaction equals -d[A]/dt = k1[A]. The rate constant k1 is a unimolecular rate constant because only one molecular species is reacting and has units of reciprocal time (s-1). For the reverse reaction, B + C ? A, the rate equals -d[B]/dt = d[A]/dt = k2[B][C]. The rate constant k2 is a bimolecular rate constant and has units of reciprocal concentration-time (M-1 s-1).
Synonym(s): velocity constants
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