For an endothermic reaction with $Δ H = + 30 kJ mo l^{- 1}$ the forward activation energy is 80 kJ/mol. A catalyst lowers the forward activation energy by 20 kJ/mol. The activation energy of the catalysed reverse reaction, in kJ/mol, is

Answer: D

Uncatalysed

E_{a, r} = E_{a, f} - Δ H = 80 - 30 = 50

kJ/mol. A catalyst lowers both barriers equally (same

Δ H

), so the catalysed value is

50 - 20 = 30

kJ/mol.