Dynamic Equilibrium and Le Chatelier's Principle (Higher)

This lesson covers reversible reactions, dynamic equilibrium and Le Chatelier's principle — all of which are Higher tier topics in the Edexcel GCSE Chemistry (1CH0) specification. Understanding these concepts is essential for explaining how industrial processes such as the Haber process are optimised. This is one of the most challenging topics in GCSE Chemistry but also one of the most rewarding once mastered.

Note: This topic is assessed at Higher tier only. Foundation tier students are not required to understand dynamic equilibrium or Le Chatelier's principle, but they should know that some reactions are reversible.

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Reversible Reactions

A reversible reaction is a reaction that can proceed in both the forward direction (reactants → products) and the backward (reverse) direction (products → reactants).

The symbol for a reversible reaction is ⇌ (two half-arrows pointing in opposite directions).

Example

The reaction between nitrogen and hydrogen to form ammonia:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

• Forward reaction: N₂ and H₂ react to form NH₃
• Backward reaction: NH₃ decomposes back into N₂ and H₂