Le Chatelier's Principle
Le Chatelier's Principle
Any factor that can affect the rate of either the forward or reverse reaction relative to the other can potentially affect the equilibrium position. The following factors can change the chemical equilibrium position of a reaction:
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concentration
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temperature
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pressure (for gaseous reactants)
It is important to understand what effect a change in one of these factors will have on a system that is in chemical equilibrium. However, performing an experiment every time to find out would waste a lot of time. Towards the end of the 1800s the French chemist Henry Louis Le Chatelier came up with principle to predict those effects.
Fact:
Henry Louis Le Chatelier.
Le Chatelier's Principle helps to predict what effect a change in temperature, concentration or pressure will have on the position of the equilibrium in a chemical reaction. This is very important, particularly in industrial applications, where yields must be accurately predicted and maximised.
Important:
\(\color{darkgreen}{\textbf{\Large Le Chatelier's Principle}}\)
When an external stress (change in pressure, temperature or concentration) is applied to a system in chemical equilibrium, the equilibrium will change in such a way as to reduce the effect of the stress.
So if the concentration of one (or more) of the reactants or products is increased the equilibrium will shift to decrease the concentration. Or if the temperature is decreased the equilibrium will shift to increase the temperature by favouring the exothermic reaction. Le Chatelier's principle is that:
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If you change the \(\color{blue}{\textbf{concentration}}\) of a reactant then the position of the equilibrium will shift to counteract that change.
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If you change the \(\color{red}{\text{temperature}}\) of the reaction the equilibrium will shift to counteract that change.
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If you change the \(\color{orange}{\textbf{pressure}}\) of the system the position of the equilibrium will shift to counteract that change.
Each of these concepts is discussed in detail in the following pages.
Optional Video: Chromate Dichromate Ion Equilibrium
The following video gives an example of Le Chatelier's principle in action.
This lesson is part of:
Chemical Equilibrium