The energies of activation for forward and reverse reaction for `A_(2)+B_(2) hArr 2AB` are `180 kJ "mol"^(-1)` and `200 kJ "mol"^(-1)` respectively. The presence of catalyst lowers the activation energy of both (forward and reverse) reactions by `100 kJ "mol"^(-1)`. The enthalpy change of the reaction `(A_(2) + B_(2) rarr 2 AB)` in the presence of catalyst will be (in `kJ "mol"^(-1)`):

Options

A. 20
B. 300
C. 120
D. 280

Answer

A

Explanation

a) A catalyst lowers only the overall activation energy for the reaction and does not affect the activation energies for the forward and the reverse reactions.
`DeltaH=E_(af)-E_(ab)`
`=180-200=-20kJ`
Ignoring the sign, the values come out to be 20 kJ `mol^(-1)`