Effect of Changing the Concentrations
When a system at equilibrium is disturbed by adding or removing one of the
substances (thus changing its concentration), all the concentrations will change
until a new equilibrium point is reached with the same value of Keq.
If the concentration of a reactant in the forward action is increased, the
equilibrium is displaced to the right, favoring the forward reaction. If the
concentration of a reactant in the reverse reaction is increased, the equilibrium is
displaced to the left. Decreases in concentration will produce effects opposite to
those produced by increases.
TIP
At equilibrium, Keq stays the same at a given temperature.Effect of Temperature on Equilibrium
If the temperature of a given equilibrium reaction is changed, the reaction will
shift to a new equilibrium point. If the temperature of a system in equilibrium is
raised, the equilibrium is shifted in the direction that absorbs heat. Note that the
shift in equilibrium as a result of temperature change is actually a change in the
value of the equilibrium constant. This is different from the effect of changing the
concentration of a reactant; when concentrations are changed, the equilibrium
shifts to a condition that maintains the same equilibrium constant.
TIP
Know how each factor affects equilibrium.Effect of Pressure on Equilibrium
A change in pressure affects only equilibria in which a gas or gases are reactants
or products. Le Châtelier’s Law can be used to predict the direction of
displacement. If it is assumed that the total space in which the reaction occurs is
constant, the pressure will depend on the total number of molecules in that space.
An increase in the number of molecules will increase pressure; a decrease in the
number of molecules will decrease pressure. If the pressure is increased, the
reaction that will be favored is the one that will lower the pressure, that is,
decrease the number of molecules.
An example of the application of these principles is the Haber process of