LeChâtelier's Principle If a stress is applied to a system at equilibrium, the system will shift in the direction which helps alleviate the stress and find a NEW EQUILIBRIUM position.

Stress causes the opposing rates to no longer be equal change in concentration change in temperature change in pressure gases ONLY adding a catalyst

Concentration Changes Increasing the concentration of a substance will shift the equilibrium in the direction which consumes that substance A + B ↔ C + D A A & B have more effective collisions between them and produce more C & D

A decrease in concentration will shift the equilibrium in the direction which produces that substance A A + B C + D

[N2] increases [NH3] increases [H2] decreases Which way will the equilibrium shift if: [N2] increases [NH3] increases [H2] decreases Answers 

Which way will the equilibrium shift if: [N2] increases RIGHT to use up extra N2 [NH3] increases LEFT to use up extra NH3 [H2] decreases RIGHT to use up extra H2

Common Ion Effect A substance containing chloride ions (ex. NaCl) is added to this equilibrium system. Which way will the equilibrium shift? Left to consume the excess Cl-1 ions What will happen to [Ag+1]? Decrease to make AgCl

Temperature Changes Increasing temperature will shift the equilibrium in the endothermic direction As heat E is added the system absorbs it

Which way will equilibrium shift if E in increased? ΔH = 53.0 kJ

Decreasing temperature will shift the equilibrium in the exothermic direction As heat E is decreased the system releases heat E

Which way will equilibrium shift if temp is decreased? ΔH = +483.6 kJ

Pressure Changes GASES ONLY An increase in pressure on the system will shift the equilibrium in the direction which produces fewer TOTAL gas molecules 2 moles gas 1 mole gas + 3 moles gas 4 moles gas

2Fe(s) + 3H2O(l) ↔ Fe2O3(s) + 3H2(g) It is NOT necessary for ALL substances to be gases for pressure to have an effect. 2Fe(s) + 3H2O(l) ↔ Fe2O3(s) + 3H2(g) Which way will the equilibrium shift if the pressure is increased?

2Fe(s) + 3H2O(l) ↔ Fe2O3(s) + 3H2(g) It is NOT necessary for ALL substances to be gases for pressure to have an effect. 2Fe(s) + 3H2O(l) ↔ Fe2O3(s) + 3H2(g) Which way will the equilibrium shift if the pressure is increased? LEFT: to the side with less gas (in this case there is NO gas on the left and 3 moles on the right. )

Decrease pressure Increase pressure

LeChatelier’s Principle Practice Relieve the stress

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