Threshold Energy
The minimum total energy that colliding molecules must possess for the collision to be capable of reaction.
Formula / equation
E_threshold = Ea + E_average
Unit
kJ/mol
In depth
Threshold energy is measured from the zero of energy rather than from the average energy of the reactants, so it exceeds the activation energy by the mean thermal energy of the molecules. The distinction matters in detailed collision-theory treatments but is often blurred in elementary discussions.
Examples in the real world
A reaction with an activation energy of 60 kJ/mol has a threshold energy a few kJ/mol higher at 298 K.