Energy Change of a Reaction
Chemistry: Cambridge International GCSE Supplement, topic 5.1.4
Chemical Bonds
All chemical bonds have a 'bond energy' that measures the strength of chemical bonds. By subtracting the total bond energies of the products from the total bond energies of reactants, we can see if a reaction is endothermic or exothermic (energy change in kJ mol-1).
Exothermic reactions
- Energy released by forming bonds > energy required to break bonds.
- I.e. overall energy change of reaction < 0.
Endothermic reactions
- Energy released by forming bonds < energy required to break bonds.
- I.e. overall energy change of reaction > 0.
Test yourself on Energy Change of a Reaction
What is the most commonly used unit for measuring bond energies?
Which of these are true about bond making and breaking?