Thermodynamics and kinetics are independent descriptions of a chemical reaction: the standard free energy change (ΔG), read on a free-energy diagram as the difference between reactant and product energy levels, states whether a conversion is spontaneous and in which direction it is favored, while the free energy of activation (Ea, ΔG‡), the energy required to reach the transient high-energy intermediate or transition state, states how fast the conversion occurs. ΔG is path-independent and reverses sign with equal magnitude when the reaction direction is reversed, whereas the activation barrier exists for both spontaneous and non-spontaneous reactions and differs in the forward and reverse directions; lower Ea means a faster reaction. This distinction belongs to biochemistry at its boundary with physical chemistry and explains the role of enzymes, which lower Ea to control reaction rate without altering ΔG — so that neither quantity alone determines whether a reaction proceeds observably.
Thermodynamics and kinetics are independent descriptions of a chemical reaction: the standard free energy change (ΔG), read on a free-energy diagram as the difference between reactant and product ene…