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The least amount of energy needed for a chemical reaction to occur. For example, striking a match on the side of a matchbox provides the activation energy, in the form of heat, necessary for the chemicals in the match to catch fire.
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|Noun||1.||activation energy - the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur; "catalysts are said to reduce the energy of activation during the transition phase of a reaction"|