Activation Energy | Definition & Facts - Britannica

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Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos activation energy Introduction References & Edit History Images Energy for exothermic reaction, endothermic reaction, and a reaction with a catalyst Potential-energy curve. The activation energy represents the minimum amount of energy required to transform reactants into products in a chemical reaction. The value of the activation energy is equivalent to the difference in potential energy between particles in an intermediate configuration (known as the transition state, or activated complex) 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. Britannica AI Icon Contents CITE verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/activation-energy Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback

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Energy for exothermic reaction, endothermic reaction, and a reaction with a catalyst
Energy for exothermic reaction, endothermic reaction, and a reaction with a catalyst (Left) In an exothermic reaction, energy is released. The reaction requires the addition of activation energy to occur. After the reaction ends, the energy of the products is lower than the energy of the reactants, so energy is released. (Center) In an endothermic reaction, energy is absorbed. The reaction requires the addition of activation energy to occur. After the reaction ends, the energy of the products is higher than the energy of the reactants, so energy is absorbed. (Right) An endothermic reaction is shown with two activation energies, one where the reaction has a catalyst and one where it does not. The catalyst lowers the amount of activation energy needed for the reaction to occur. (more)
activation energy chemistry Ask Anything Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Nov. 14, 2025 •History Britannica AI Icon Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

activation energy, in chemistry, the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport.

In transition-state theory, the activation energy is the difference in energy content between atoms or molecules in an activated or transition-state configuration and the corresponding atoms and molecules in their initial configuration. The activation energy is usually represented by the symbol Ea in mathematical expressions for such quantities as the reaction rate constant k, k = A e ( - E a / R T ) ,where A is the pre-exponential factor, which describes how often collisions occur and is different for each reaction; R is the universal gas constant, which is about 8.314 joules per kelvin per mole; and T is the temperature in kelvin. Activation energy is also represented by Ea in the expression for the diffusion coefficient D, D = D 0 e ( - E a / R T ) ,where D0 is a constant.

Activation energies are determined from experimental rate constants or diffusion coefficients that are measured at different temperatures.

energy levels of a luminescent centre More From Britannica luminescence: Sulfide-type phosphors, activators, fluxes The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.

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