You are presented with the question "What must a chemical reaction overcome before starting?" and the following answer choices: 
- PV=nRT
 - heat or cold
 - reactants
 - energy barrier
 - Dehydration
 - harmful substances
 - resistance
 - temperature

Now knowing that all chemical reactions require activation energy to get started and activation energy is required to overcome the energy barrier, choose the best answer.


 

    energy barrier     