Unit 7: Equilibrium And Acids

Section 4: LeChatelier's Principle an It's Applications

LeChatelier's Principle

Changing The Concentration

Adding An Inert Gas

Changing The Volume Of A Container

Change In Temp

LeChatelier's Principle

LeChatelier was a scientist that came up with his own idea that describes how equilibrium will change to compensate for an increase, decrease, or basically changing the conditions of the equilibrium. LeChatelier's Principle states: if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in the direction that tends to reduce the change.

Changing Concentration

If you have a reaction at equilibrium and you decrease the concentration by removing some of that substance, the reaction will shift towards the removed substance. Likewise, if the reaction is at equilibrium and you increase the concentraion of a substance by adding some of the that substance, then the reaction will shift away from the increased substance.

Adding An Inert Gas

If you add an inert gas to increase the total pressure of the system, nothing will change. The equilibrium pressure will NOT change. (Note: teachers like to ask about this, too!)

Changing The Volume Of A Container

If a reaction at equilibrium has a pressure change due to an increase or decrease in container size, then the equilibrium position will change. If the container size increases then the reaction will proceed towards the side with the most number of gaseous moles. If the container size decreases then the reaction will proceed towards the side with the least number of gaseous moles.

Change In Temperature

If a reaction at equilibrium has a temperature change due to an increase or decrease in the temperaure of the system, then the equilibrium position will change. If the temperature increases then the reaction will proceed toward the side that consumes energy. For example, in the equation:

the reaction will proceed to the left (towards the side consuming energy.)

Likewise, if the temperature is decreased, then the reaction will proceed toward the side that does not consume energy (Exactly opposite that of the above example.) (Note: Please note that the equilibium position will change but the equilibrium constant will NOT change with a change in temperature.)