Define Reaction Rate constant

Reaction Rate constant

The reaction rate constant is defined as the rate of reaction when the concentration of each of the reactants is unity.

• It is also called as the specific rate constant.
• It is the measure of the rate of reaction when all the reactants  are at a unit concentration
• Hence

Rate of reaction = k* (function of concentrations of reactants)

• If we assume that the concentrations are equal to unity, then

                     A rate of reaction = k

                                           where k is rate constant

• The rate constant depends on temperature and it increases with temperature.
• The unit of k depends upon the units of concentration and time.
• If we measure the concentration in moles/lit (mol/l) and time (s)

Unit of k for nth-order reaction

• Hence,
• The unit of k for nth-order reaction = (time)^-1 (concentration ) ^1-n

For first order reaction

n = 1

Unit of k= (time)^-1

= (s)^-1

For second order reaction

n=2

Unit of k =(time)^-1 (concentration ) ^-1

=(s)^-1*(mol/l)^-1

= l/(mol*s)