Activation energy: definition in chemistry
Activation energy: The minimum energy that colliding particles must have for a reaction to take place, given the symbol Eₐ.
Activation energy acts like a hill that the reactants must climb before they can turn into products, even when the reaction releases energy overall. Reactions with a high activation energy are slow at room temperature, which is why paper does not catch fire by itself. Raising the temperature gives more particles enough energy to react, and a catalyst speeds up a reaction by offering a route with a lower activation energy.
Examples
- Striking a match supplies the energy to start it burning
- A spark ignites the fuel–air mixture in a car engine
- Enzymes lower activation energies so reactions in cells run at body temperature
- Hydrogen and oxygen can sit mixed without reacting until a spark sets them off