- For spontaneous reactions, the energy state of the products will be lower than that of the reactants (negative ΔG). For most reactions, the intermediate transition state will be higher than the energy level of the reactants (also called the 'ground' state)
- The difference in energy between the ground state and the transition state is called the activation energy
- In a number of ways, enzymes are able to accelerate the rate of a reaction by lowering the activation energy (the barrier to the progress of a reaction)
- In the absence of enzyme, the reactants will only interact through random collisions. Out of the total set of collisions in a given time, only a small fraction will have the necessary velocities and orientations sufficient to 'cross' the transition state barrier