Page 87 - Instant notes

Fundamentals of equilibria 73

These are all examples of Le Chatelier’s Principle, which states that:

‘when a system at equilibrium is subjected to a disturbance, the
composition adjusts to minimize the effect of this disturbance.’

Thus, when a chemical species that forms part of the equilibrium reaction is added to the
system at equilibrium, reaction occurs to remove that species. Also when the total
pressure of a system involving gases at equilibrium is increased, the system adjusts to
reduce the total number of moles of gas (and hence the volume) and offset this pressure
increase. Finally, when the temperature of a system is increased, the system adjusts to
take in energy and reduce this temperature increase. This is a useful principle that allows
the effect of any perturbation on the equilibrium to be predicted.