Fact 1: All chemical reactions require activation energy to get started.

Fact 2: Activation energy is required to overcome the energy barrier.

Given the two facts above, answer the question "What must a chemical reaction overcome before starting?" with the following options: 
- PV=nRT
 - heat or cold
 - reactants
 - energy barrier
 - Dehydration
 - harmful substances
 - resistance
 - temperature


 

    energy barrier     