Bond Energy Calculations (Higher)

This lesson covers bond energy calculations, which is a Higher tier topic in the Edexcel GCSE Chemistry (1CH0) specification. You will learn why bond breaking is endothermic and bond making is exothermic, how to use bond energy data to calculate the overall energy change of a reaction, and how to determine whether a reaction is exothermic or endothermic from the calculation. This is a very commonly examined topic at Higher tier.

Note: This topic is assessed at Higher tier only. Foundation tier students do not need to carry out bond energy calculations, but understanding the general principles of bond breaking and bond making is useful for all students.

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Bond Breaking and Bond Making

During a chemical reaction:

1. Bonds in the reactants must be broken — this requires energy to be put in (it is an endothermic process).
2. New bonds in the products are formed — this releases energy (it is an exothermic process).

The overall energy change of a reaction depends on the balance between these two processes.