This guide covers IGCSE Chemistry topic 6: energy changes in chemical reactions. You will revise exothermic (heat given out; temperature rise) and endothermic (heat taken in; temperature fall), bond breaking (endothermic) and bond making (exothermic), and energy level diagrams.

Key concepts to revise

• Exothermic – Heat given out to surroundings; temperature of mixture rises; products have less energy than reactants (e.g. combustion, neutralisation).
• Endothermic – Heat taken in from surroundings; temperature of mixture falls; products have more energy than reactants (e.g. thermal decomposition, photosynthesis).
• Bond breaking – Requires energy (endothermic); bond making – releases energy (exothermic).
• Energy level diagram – Reactants and products; exothermic: products lower; endothermic: products higher; activation energy (peak).

Exam tips and command words

• State – Whether a reaction is exothermic or endothermic from a description or diagram.
• Describe – What happens to temperature in exothermic and endothermic reactions.
• Explain – Why bond breaking is endothermic (energy needed to break bonds); why bond making is exothermic (energy released).
• Draw – An energy level diagram for an exothermic or endothermic reaction; label activation energy and overall change.

Common mistakes

• Confusing exothermic (heat out; temperature rises) with endothermic (heat in; temperature falls).
• Saying “bonds store energy” (breaking bonds uses energy; making bonds releases energy).
• Not labelling activation energy on the diagram (energy from reactants to top of curve).

Revision checklist

• Define exothermic and endothermic and give one example of each.
• Describe what happens to temperature in exothermic and endothermic reactions.
• Draw an energy level diagram for exothermic and endothermic; label activation energy.
• Explain bond breaking (endothermic) and bond making (exothermic) in terms of energy.

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise energy change questions, or explore Tutopiya’s learning portal for more revision resources.