The reaction is not spontaneous at any temperature. The reaction is spontaneous at a temperature above a certain critical temperature. The reaction is spontaneous at a temperature below a certain critical temperature. All exothermic reactions occur spontaneously. When an exothermic reaction occurs, the temperature decreases.
All endothermic reactions occur spontaneously.
The top of the barrier corresponds to the transition state. The size of E 1 and E 2 can be affected by the presence of a catalyst. The thermodynamic spontaneity of the reaction is affected by E 1 . The heat absorbed in the reaction corresponds to E 3 . An increase in T would increase the reaction rate.