Course Introduction This course covers C2.5 Exothermic and endothermic reactions, which is examined on Paper 2 of the GCSE AQA Chemistry Course. The following information, included this course, is examined at Higher Tier only: How to calculate the energy transferred in reactions using supplied bond energies. In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds. In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.