Q.In a chemical equilibrium, the rate constant for the forward reaction is $2.5 \times 10^2$ and the equilibrium constant is 50. The rate constant for the reverse reaction is,

In 1864, the Norwegian chemists Cato Maximilian Guldberg and Peter Waage generalised the experimental behaviour of many reversible reactions into the law of mass action:

"At any instant, the rate of a chemical reaction at a given temperature is directly proportional to the product of the active masses of the reactants at that instant."

For a single reactant with stoichiometric coefficient x, this reads $\text{Rate}\propto[\text{Reactant}]^x$, where the square brackets denote active mass -- molar concentration, $n/V$, in mol dm$^{-3}$ (or mol L$^{-1}$), with n the number of moles and V the container's volume. …