the.com/activation energy

means The minimum energy a chemical reaction needs to get started, even if the reaction will release energy overall once it's underway.

from Coined within chemistry as part of the vocabulary of reaction kinetics, where it describes the energy barrier reactants must surmount to reach the unstable 'transition state' before they can become products. The concept is tied to the Arrhenius equation, formalized in the late 19th century by Svante Arrhenius, who gave the hump a name and a number rather than inventing the idea of barriers itself — chemists had long sensed that some reactions needed a 'push' to start even if they'd happily release heat afterward, like a match needing a strike before a fire that burns on its own.