ChemStd 9a: Le Chatelier's Principle

First of all, what is Le Chatelier's principle? If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

In essence, whatever is added to the equation or shifts the equilibrium, Le Chantelier's principle states that the equation will automatically shift to counter this change and maintain an equilibrium; it will do exactly the opposite of whatever is disrupting the equilibrium.

• Effect of the change in concentration:

CO + 2 H₂ ⇌ CH₃OH

If more CO was added, then according to Le Chantelier's principle, the amount of CH₃OH would increase also. Whenever there is a change in concentration, the opposite side of the equation will experience a similar change, whether a decrease or increase of molecules.

• Effect of the change in temperature:

N₂ + 3 H₂ ⇌ 2 NH₃ + 92kJ

In the above equation, it shows heat is part of the product, making this an exothermic reaction. If the temperature increases, the equilibrium will shift to the side that does not have heat to create a balance and decrease the temperature, which is to the left. Decreasing the temperature will shift the equilibrium left, towards the reactant.

H₂(g) +I₂(s) + 52 kJ ⇌ 2HI(g)

In this equation, heat is part of the reactant, making this an endothermic reaction. Increasing the temperature will cause shift the equilibrium right, however, decreasing the temperature, shifts the equilibrium toward the left to balance the equation at a constant temperature.

• Effect of the change in pressure:

2NO₂(g) ⇌ N₂O₄(g)
An increase in pressure results in a shift towards the side with the least molecules, which is N₂O_{4. A decrease in pressure however causes the equilibrium to shift to the side with more molecules to counter the decrease in molecules and maintain an equilibrium; in this case} 2NO_2.

For a full complete explanation of Le Chantelier's Principle:
http://www.youtube.com/watch?v=Ywzvzw6Rdpk