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.
What a learner can do afterwards
- 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
1 · Read
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.
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.
Equal rates freeze concentrations, systems push back on change, and industry trades yield for speed.
More to read
13.1 Chemical Equilibria
Equilibrium is a busy standstill. In sealed flasks, forward and reverse reactions run at matching speeds, so concentrations freeze while molecules keep swapping. Open the flask and gases flee, breaking balance. Reaching it takes minutes or millennia.
13.3 Shifting Equilibria: Le Châtelier’s Principle
Disturbed equilibria fight back. Add reactant and the system makes more product; raise pressure and it favours fewer gas molecules; heat an exothermic reaction and it retreats. Le Chatelier predicts each shift: oppose the change. Ammonia plants tune heat and pressure around these rules, adding an iron catalyst for speed.
13.2 Equilibrium Constants
Constants measure the split. Big K means products dominate, tiny K means reactants rule. Values shift with temperature alone: concentration changes disturb position, never the constant. Compare K across reactions to rank completeness.
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Where it sits
Optional connections
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.