activation energy

American  

noun

Chemistry.

1. the least amount of energy required to activate atoms or molecules to a state in which they can undergo a chemical reaction.

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activation energy Scientific  

/ ăk′tə-vā′shən /

1. The least amount of energy needed for a chemical reaction to take place. Some elements and compounds react together naturally just by being close to each other, and their activation energy is zero. Others will react together only after a certain amount of energy is added to them. Striking a match on the side of a matchbox, for example, provides the activation energy (in the form of heat produced by friction) necessary for the chemicals in the match to ignite. Activation energy is usually expressed in terms of joules per mole of reactants.

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Etymology

Origin of activation energy

First recorded in 1920–25

Example Sentences

For example, swapping chlorophyll and pheophytin in D2 could overcome the electron block, because chlorophyll needs lower activation energy than pheophytin.

From Science Daily • Oct. 13, 2025

Specifically, the transfer of electrons from pheophytin to plastoquinone in D2 requires twice as much activation energy as D1 -- a barrier that electrons seem unable to overcome, preventing energy from flowing forward.

From Science Daily • Oct. 13, 2025

The activation energy of ionic conduction of this material is extremely low, and the ionic conductivity of this material at low temperature is one of the highest among known solid electrolytes, including sulfide-based materials.

From Science Daily • Apr. 2, 2024

If the activation energy is much smaller than the average kinetic energy of the molecules, a large fraction of molecules will be adequately energetic and the reaction will proceed rapidly.

From Textbooks • Feb. 14, 2019

The enzyme-substrate complex can also lower activation energy by compromising the bond structure so that it is easier to break.

From Textbooks • Apr. 25, 2013