What is order of reaction? Write unit of rate constant $K$ for the zero order, first order and second order reaction.

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Solution

The order of a reaction is define as the sum of all the powers to which concentration terms in the rate law are raised to express the observed rate of the reaction.
Rate constant $K$ for the zero order:
$K = \frac{M o l e {l i t r e}^{- 1} {S e c o n d}^{- 1}}{{(C o n c e n t r a t i o n)}^{0}}$
$= M o l e {L i t r e}^{- 1} {S e c o n d}^{- 1}$
Rate constant $k$ for the first order:
$K = \frac{M o l e {l i t r e}^{- 1} {S e c o n d}^{- 1}}{{(C o n c e n t r a t i o n)}^{1}}$
$= \frac{M o l e {l i t r e}^{- 1} {S e c o n d}^{- 1}}{M o l e {L i t r e}^{- 1}}$
$= {S e c o n d}^{- 1}$
Rate constant $k$ for the second order:
$K = \frac{M o l e {l i t r e}^{- 1} {S e c o n d}^{- 1}}{{(C o n c e n t r a t i o n)}^{2}}$
$= \frac{M o l e {L i t r e}^{- 1} {S e c o n d}^{- 1}}{{(M o l e {L i t r e}^{- 1})}^{2}}$
$= \frac{M o l e {L i t r e}^{- 1} {S e c o n d}^{- 1}}{{M o l e}^{2} {L i t r e}^{- 2}}$
$= {M o l e}^{- 1} L i t r e {S e c o n d}^{- 1}$

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