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.
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