What would be an appropriate unit for the rate constant of a second-order reaction?

s^{- 1}

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m o l L^{- 1}

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m o l L^{- 1} s^{- 1}

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L {m o l}^{- 1} s^{- 1}

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{m o l}^{2} L^{- 2} s^{- 2}

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Solution

The correct option is D $L {m o l}^{- 1} s^{- 1}$
The equation for the rate of a second-order reaction is calculated as follows:

Rate $=$ $k$ $[A]^{2}$ , where $k$ is the rate constant of the reaction and $[A]$ is the concentration of the reactant at any instant. It is raised to the power of 2, because, it is a second-order reaction.

Unit for Rate is $\frac{c o n c}{t i m e}$ that is $m o l$ $L^{- 1}$ $s^{- 1}$ . We need to find the unit of $k$ . Unit of $[A]^{2}$ is $(c o n c)^{2}$ that is $m o l^{2} L^{- 2}$ .

Putting all these in the equation, we have,

$m o l$ $L^{- 1}$ $s^{- 1}$ $=$ $(k)$ $m o l^{2} L^{- 2}$

Thus $k$ $=$ $L m o l^{- 1} s^{- 1}$

Option D is the correct answer.

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