Question

What is the order of reaction whose rate constant has the same units as the rate of reaction?

Answer 1

Order of the reaction.

• The order of a reaction is defined as the sum of the powers of the concentration terms of the reactants in the experimentally determined rate equation for the reaction.
• If the rate equation for the reaction is: $\mathrm{r}=k{\left[\mathrm{A}\right]}^x{\left[\mathrm{B}\right]}^y$

where;

r=rate of reaction

k=rate constant

[A], [B]=concentrarions of reactants A and B respectively.

• We may say that the reaction is of order ‘x’ with respect to reactant A and of order 'y' with respect to reactant B.
• Therefore, the overall order of the reaction, $\mathrm{n}=\mathrm{x}+\mathrm{y}$
• The rate constant and the rate of reaction will have the same unit when $\text{'}\mathrm{x}+\mathrm{y}\text{'}$will be zero.
• That is, ‘x’ should be zero, and ‘y’ should be zero for a reaction.
• So, zero will be the order of the reaction whose rate of reaction and rate constant has the same unit.
• For a zero-order reaction, the unit of $\mathrm{k}=\mathrm{mol}{\mathrm{L}}^{-1}{\mathrm{s}}^{-1}\mathrm{or}\mathrm{mol}{\mathrm{dm}}^{-3}{\mathrm{s}}^{-1}$

Therefore, zero is the order of reaction whose rate of reaction and rate constant has the same unit.