---
title: "Reversible Reactions, Dynamic Equilibrium and Le Chatelier"
description: "Some reactions run both ways at once. In a closed container the forward and backward rates settle equal, and changing temperature, pressure or a concentration shifts the position until the rates match"
canonical: https://lightmysky.com/learn/science/reversible-reactions-dynamic-equilibrium-and-le-chatelier-mt_Zas-V3kTiR
source: https://lightmysky.com/learn/science/reversible-reactions-dynamic-equilibrium-and-le-chatelier-mt_Zas-V3kTiR.md
retrieved: 2026-09-12
---

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# Reversible Reactions, Dynamic Equilibrium and Le Chatelier

Some reactions run both ways at once. In a closed container the forward and backward rates settle equal, and changing temperature, pressure or a concentration shifts the position until the rates match again.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/reversible-reactions-dynamic-equilibrium-and-le-chatelier-mt_Zas-V3kTiR

## Ready when they can

- Uses the reversible arrow and explains what is still happening at equilibrium
- Explains why one direction is exothermic and the other endothermic, using a reversible example such as hydrated copper sulfate
- Predicts the shift when temperature, pressure or a concentration is changed, and justifies it
- Explains why an industrial process such as the Haber process runs at compromise conditions rather than the ones equilibrium alone would pick

## Lesson: The standstill that keeps moving

Some reactions run both ways at once, shown with a reversible arrow. In a closed container the forward and backward rates settle equal. Concentrations then freeze, yet molecules keep swapping both ways. That busy standstill is dynamic equilibrium. Open the flask and escaping gases break the balance.

The two directions carry opposite heat. Heat blue hydrated copper sulfate and it drives water off to white powder, taking heat in. Add water back and it reverses, giving heat out. One way is endothermic and the other is exothermic, always.

Le Chatelier predicts how a disturbed system pushes back. Add a reactant and it makes more product. Raise the pressure and it favours the side with fewer gas molecules. Heat an exothermic reaction and it retreats towards reactants, favouring the endothermic way.

**Tip.** The Haber process for ammonia, N2 + 3H2 going to 2NH3, runs at compromise conditions. High pressure helps yield since four gas molecules become two, but extreme pressure costs too much. Cold would give the best yield yet crawl, so moderate warmth trades some yield for speed. An iron catalyst hurries both ways without moving the final split.

**Recap.** Equal rates freeze concentrations, systems push back on change, and industry trades yield for speed.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Rates of Reaction: Collision Theory and What Changes a Rate](https://lightmysky.com/learn/science/rates-of-reaction-collision-theory-and-what-changes-a-rate-mt_Ma2bOotr9g)
- [Reactions That Release or Absorb Heat](https://lightmysky.com/learn/science/reactions-that-release-or-absorb-heat-mt_UoqUPI_uNz)

## Opens up

- [The Equilibrium Constant Kc](https://lightmysky.com/learn/science/the-equilibrium-constant-kc-mt_3G8b6Hyz3u)
- [The Haber Process and the Industrial Compromise](https://lightmysky.com/learn/science/the-haber-process-and-the-industrial-compromise-mt_J-JkijqnY5)