Britannica Sources used in this answer

How does activation energy affect whether molecular collisions lead to a reaction?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A graph showing a potential energy curve for a chemical reaction, with the y-axis labeled potential energy and the x-axis labeled progress of reaction. The curve rises from the initial state (reactants) to a peak labeled transition state (activated complex), indicating activation energy, then drops to the final state (products). — chemical kinetics In the Arrhenius equation, the activation energy (E) represents the minimum amount of energy required to transform reactants into products in a chemical reaction. On a potential energy curve, the value of the activation energy is equivalent to the difference in potential energy between particles in an intermediate configuration (known as the activated complex, or transition state) and particles of reactants in their initial state. The activation energy thus can be visualized as a barrier that must be overcome by reactants before products can be formed.

In chemical kinetics, activation energy ( $E_{a}$ ) acts as a critical energy barrier that determines whether a molecular collision results in a chemical reaction.12

According to collision theory, not every collision between molecules leads to a reaction. For a collision to be effective, the reacting species must meet two primary criteria:3
* Energy Requirement: The colliding molecules must possess a minimum amount of internal energy equal to or greater than the activation energy. This energy is necessary to initiate the bond-breaking and bond-forming processes required to reach the transition state.342
* Orientation: The molecules must be oriented in a manner favorable to the necessary rearrangement of atoms and electrons.34

If the kinetic energy of the colliding molecules is less than the activation energy, the collision is ineffective, and the molecules simply separate unchanged. Because the fraction of molecules possessing energy greater than $E_{a}$ increases with temperature, higher temperatures lead to a greater number of effective collisions, thereby increasing the reaction rate.24