In gaseous reactions important for the understanding of the upper atmosphere $H_{2} O$ and o react bimolecularly to form two OH radicals. $∆ H$ for this reaction is $72 kJ {mol}^{- 1}$ at 500 K and $E_{a}$ is $77 K j {mol}^{- 1}$ then $E_{a}$ for the bimolecular recombination of two OH radicals to form $H_{2} O$ and O is :

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$5 kJ {mol}^{- 1}$

$7 kJ {mol}^{- 1}$

$3 kJ {mol}^{- 1}$

$4 kJ {mol}^{- 1}$

answer is C.

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Detailed Solution

Given,

$∆ H$ for this reaction = $72 kJ {mol}^{- 1}$ at 500 K

$E_{a}$ = $77 K j {mol}^{- 1}$ .

Now we have,

$\begin{array}{l} ΔH = E_{af} - E_{ab} \\ 72 = 77 - E_{ab} \\ E_{ab} = 77 - 72 \\ E_{ab} = 5 kJ {mol}^{- 1} \end{array}$

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