professor Dave here let's talk about Le Chatelier's principle. Le Chatelier's principle says that if you induce a stress on a system at equilibrium the equilibrium will shift so as to relieve that stress. so let's see some examples of a stress we could put on a system at equilibrium.
first we could modify the concentration of any of the compounds. let's say we add some of this reactant, that will unbalance the equilibrium and the forward reaction will speed up to use up some of the additional reactants and turn them into products and restore equilibrium. the equilibrium is said to have shifted right.
if we add more products it would shift left. likewise if we selectively remove one of the components the equilibrium will shift to produce more of that species to restore balance. that is one type of stress we could put on a system.
another stress would be to change the temperature. to see how this would affect an equilibrium we have to see whether a given reaction is exothermic or endothermic. this tells us whether a reaction absorbs or releases energy and is signified by delta H the change in enthalpy.
if delta H is negative the reaction is exothermic and releases energy so we could think of heat energy as a product of this reaction. if instead it's positive that means it's endothermic and energy must be absorbed for the reaction to go. so we could think of heat energy as a reactant in that scenario.
once we translate thermochemical data in this way we can treat the word heat as just another substance involved in the reaction higher temperature means more heat so things will shift to the other side to use up some excess heat and relieve the stress. cooling it down would have the opposite effect. the third stress we can examine is changing the volume or pressure.
let's say the equilibrium involves gases in a balloon what if we decrease the volume? if we remember Boyle's law we know that the pressure will go up since the smaller the volume the more the particles will hit the sides and exert pressure. if there is a discrepancy in the number of moles of particles on either side of the equilibrium it will shift towards the side with fewer particles so as to alleviate some of the additional pressure.
in this equilibrium between a diatomic molecule and two monoatomic species the right side has twice as many particles so shifting left means atoms fusing together resulting in fewer particles which lowers the pressure on the container. if we increase the volume thereby lowering the pressure the equilibrium would shift towards the side with more particles in order to regain some of the lost pressure. let's check comprehension.
