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 "overcoming the energy barrier starts a what" with the following options: 
- chemical reaction
 - contraction
 - Movement of an air mass
 - expansion
 - metabolic reaction
 - energy storage
 - increased body strength
 - oxidation reaction


 

 chemical reaction        