Kinetics deals with 'what rate and whether a particular reaction will take place.
There are many thermodynamically favorable reactions that do not occur spontaneously.
Some reactions may be thermodynamically feasible, but kinetically improbable.' This phenomenon, called a kinetic barrier, is caused by the existence of unstable transition states (activated complexes). These are formed only when a larger amount of energy is supplied (the formation of an activated complex is thermodynamically unfavorable). This additional energy is called activation energy' (EA).