3.26 Activation Energy
3.26 Activation Energy
- Define activation energy.
- Explain why all chemical reactions require activation energy.
These cheerleaders have a lot of energy! Their role is to get the fans as excited as they are so everyone will cheer for
the team. They use their energy to activate the crowd.
Getting Started
Chemical reactions also need energy to be activated. They require a certain amount of energy just to get started.
This energy is calledactivation energy. For example, activation energy is needed to start a car engine. Turning the
key causes a spark that activates the burning of gasoline in the engine. The combustion of gas won’t occur without
the spark of energy to begin the reaction.
Q:Why is activation energy needed? Why won’t a reaction occur without it?
A:A reaction won’t occur unless atoms or molecules of reactants come together. This happens only if the particles
are moving, and movement takes energy. Often, reactants have to overcome forces that push them apart. This takes
energy as well. Still more energy is needed to start breaking bonds in reactants.
Activating Endothermic and Exothermic Reactions
Some chemical reactions need a constant input of energy to take place. They are called endothermic reactions.
Other chemical reactions release energy when they occur, so they can keep going without any added energy. They
are called exothermic reactions.