`H_(2)O` and O-atom react in upper atmosphere bimolecularly to form two OH radicals. `DeltaH` for the reaction is 72 kJ at 500 K and energy of activation is 77 kJ `"mol"^(-1).E_(a)` for bimolecular recombination of two OH radicals to form `H_(2)O` and O-atom, will be

Options

A. 5 kJ `" mol"^(-1)`
B. 72 kJ `" mol"^(-1)`
C. 77 kJ `" mol"^(-1)`
D. 149 kJ `" mol"^(-1)`

Answer

A

Explanation

`H_(2)O+Ooverset(E_(a))rarr2OH,DeltaH=72kJ`
`2OHoverset(E_(b))rarrH_(2)O+O,DeltaH=-72kJ`
Also `E_(a)-E_(b)=DeltaH" or "77-E_(b)=72`
`therefore" "E_(b)=5kJ" mol"^(-1)`