Key concepts:

• The flame burning at the top of a candle is a spontaneous chemical reaction taking place.
• Oxygen and hydrocarbon waxes are reacting to produce carbon dioxide and water.
• At the start of the reaction the oxygen gas and the hydrocarbon wax are both rich in potential energy, they are at the top of the energy " hill ".
• As the reaction takes place energy is given off, and carbon dioxide and water molecules are produced.
• At the end of the reaction the product molecules (carbon dioxide and water) are low in energy, they are at the bottom of the energy " hill ".
• It is a spontaneous reaction for the flame in the candle to burn, and it obeys the Second Law of Thermodynamics.