# rate constants

(redirected from velocity constants)

## rate con·stants (k),

proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); for example, 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 (for example, 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 (for example, M-1 s-1).
Synonym(s): velocity constants
Farlex Partner Medical Dictionary © Farlex 2012

## rate con·stants

(k) (rāt kon'stănts)
Proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); e.g., 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, since there is only one molecular species reacting, and has units of reciprocal time (e.g., sec-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 (e.g., m-1 sec-1).
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
where t[s] is time, [c.sub.x] [mol] is concentration of substance X, V[[m.sup.3]] is volume of the reactor, [q.sub.a] [[m.sup.3][s.sup.-1]] and qb [[m.sup.3][s.sup.-1]] represent volumetric flow rates, [k.sub.1] [[s.sup.-1][mol.sup.-1]], [k.sub.2] [[s.sup.-1]] and [k.sub.3] [[s.sup.-1][mol.sup.-1]] are velocity constants. Their values are unknown and have to be estimated or determined experimentally.
These parameters can be changed in appropriate edit boxes as well as volume of the reactor, velocity constants etc.
[v.sub.o] and [v.sub.s] are the reaction initial and steady-state velocities, respectively, and [k.sub.app] denotes the apparent first-order velocity constant for interconversion between [v.sub.o] and [v.sub.s].
The reaction progress curves for the unpreincubated system were concave downward (Figure 4(a)), indicating that the velocity of urea hydrolysis decreased from an initial velocity ([v.sub.o]) to a much slower steady-state velocity ([v.sub.s]) according to the apparent first-order velocity constant [k.sub.app].

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