When a chemical reaction reaches a state of equilibrium, the density of the reactants and products remain stable indefinitely, only if the conditions of the system remain fixed. But, if any of them change, the system develops a new state of equilibrium with the consequent variation. All these observations were taken into account to develop Le Chatelier's principle.
This postulate was formulated for the first time in 1884, by the chemist Henri-Louise Le Chatelier, who used it to evaluate the consequences that these changes cause.
Le Chatelier's principle establishes that: when a variation arises in any of the conditions present in an equilibrium system, said system will proceed to regain equilibrium, rejecting the cause that originated the variation.
Below are some of the causes that could cause an alteration of the chemical balance:
- Variation in pressure: a change in pressure will only affect the equilibrium, if some gaseous substance participates in the reaction. Changes in pressure do not affect much the concentration of liquids or solids, since these are not usually compressed. However in gases, if relevant changes originate.
- Variation in temperature: an increase in temperature causes the equilibrium to be directed towards the absorption of heat and thus counteract the increase in temperature. If the temperature drops, it causes the equilibrium to move in such a way that the system releases heat.
- Variation in concentration: as the concentration of a substance increases, it causes the balance to develop and reduces the existing amount of that substance. Now if the concentration decreases, then the balance will move towards the creation of that substance, that is, the system develops, allowing the appearance of a greater amount of the substance that has been reduced in concentration.
