The reaction A → P consists of the following three elementary steps with their respective activation energies
A → I (fast), Ea,1
I → A (fast), Ea,2
I → P (slow), Ea,3
Activation energy of the overall reaction is
1
Ea,1 + Ea,2 + Ea,3
2
Ea,1 + Ea,2 - Ea,3
3
Ea,2
4
Ea,1 - Ea,2 + Ea,3