Key concepts:

• A candle is made of long hydrocarbon molecules holding a lot of potential energy.
• Surrounding the candle are molecules of oxygen gas, also holding a lot of potential energy.
• The flame at the top of a burning candle is a chemical reaction taking place between these two types of molecules.
• In this reaction, the oxygen molecules are crashing violently into the molecules of wax (hydrocarbons).
  This causes the molecules to break apart and rearrange themselves into new molecular combinations.
• The new molecules formed at the end of the reaction are carbon dioxide and water.
• During the reaction, energy is given off into the environment in the form of light and heat.
• This reaction is obeying the second law of thermodynamics and is spontaneous.