The energies of activation for forward and reverse reactions for

\(A_2 + B_2\)⇌\(2AB\)

are 180 kJ mol^–1 and 200 kJ mol^–1 respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol^–1. The enthalpy change of the reaction \((A_2 + B_2 \rightarrow 2AB)\) in the presence of catalyst will be (in kJ mol^–1):

20

The correct answer is option 3. 20

To determine the enthalpy change of the reaction in the presence of a catalyst, we can use the fact that the enthalpy change (\(\Delta H\)) is independent of the presence of a catalyst. The enthalpy change remains the same whether or not a catalyst is present.

The enthalpy change (\(\Delta H\)) can be calculated using the equation:

\(\Delta H = \text{Activation Energy (Reverse)} - \text{Activation Energy (Forward)}\)

Given that the energies of activation for the forward and reverse reactions are 180 kJ/mol and 200 kJ/mol, respectively, and the presence of a catalyst lowers the activation energy of both reactions by 100 kJ/mol, we can substitute these values into the equation:

\(\Delta H = (200 \, \text{kJ/mol} - 100 \, \text{kJ/mol}) - (180 \, \text{kJ/mol} - 100 \, \text{kJ/mol})\)

\(\Delta H = 100 \, \text{kJ/mol} - 80 \, \text{kJ/mol}\)

\(\Delta H = 20 \, \text{kJ/mol}\)

Therefore, the correct answer is (3) 20 kJ/mol.