What is Le Chatelier's principle and how is it used?
When a system has reached a dynamic equilibrium at a given concentration of reactants/products, temperature, pressure and volume, then a change in any of those factors will change the rate of the reaction in the direction which moves the reaction to a new equilibrium. I.e. the RoR will change to counteract changes in the system. For example, given the following reaction at equilibrium: A + B <=> C If I increase the concentration of reactants A and B, then the rate of the forward reaction will increase. This happens because there more are molecules of A and B relative to molecule C, favouring the forward reaction (as more opportunities for successful collisions between A and B). So the forward rate increases. Another example, with the same formula. Let's assume we know that the forward reaction is exothermic. If we increase the temperature of the system, it will favour the direction which decreases the temperature, i.e. the backward reaction will be favoured. So, by Le Chatelier's Principle, the backward reaction rate increases.
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