What is Le Chatelier's Principle?

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The principle states that, if any system in dynamic equilibrium is subjected to a change, a process will act to minimise the change to restore equilibrium.


These changes could be in concentrations, pressure or temperature. The following reaction can be used to demonstrate this:

N2(g) + 3H2(g) <-> 2NH3(g)     (exothermic)

1. Concentration: An increase in the concentration of a reactant will be countered by a shift in eqiulibrium to the right - the product side. This will remove reactant and so decrease the concentration again.

2. Pressure: An increase in total pressure will cause a shift in equilibrium to the right - the side with least moles of gas. As there are less moles of gas in the product, this will reduce the pressure again.

3. Temperature: A decrease in temperature will cause a shift in equilibrium to the right - the exothermic direction. As an exothermic reaction releases heat, this will increase the temperature to counter the original change.

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