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.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial