A describes opportunity; the exponential describes how much of that opportunity survives the barrier.

The Arrhenius equation describes how the rate of a chemical reaction changes with temperature. It relates the reaction’s rate constant to temperature, activation energy, and a frequency factor, commonly written as k = Ae^−Eₐ/RT. Its key message is simple: hotter molecules are more likely to possess enough energy to cross the reaction’s activation barrier. Even modest temperature changes can therefore produce dramatic changes in reaction speed. The equation gives chemists a practical way to estimate activation energies and predict how rapidly reactions proceed under different conditions. It is used primarily in chemical kinetics, chemical engineering, and materials science.