High Quality Content by WIKIPEDIA articles! The distinction (also known as selectivity) between kinetically or thermodynamically controlled chemical reaction pathways is relevant when product A forms faster (which is called the kinetically controlled product) than product B because the activation energy for product A is lower than that for product B, yet product B is more stable (this is called the thermodynamically controlled product). The conditions of the reaction, such as temperature, pressure, or solvent, affect which reaction pathway may be favored: either the kinetically controlled or the thermodynamically controlled one. Note this is only true if the activation energy of the two pathways differ, with one pathway having a lower Ea (energy of activation) than the other.