Answer the following question given this paragraph: 

Chemical reactions also need energy to be activated. They require a certain amount of energy just to get started. This energy is called activation 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: What do chemical reactions  need to be activated?


A:
energy