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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.
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Stress causes the opposing rates to no longer be equal
change in concentration change in temperature change in pressure gases ONLY adding a catalyst
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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
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A decrease in concentration will shift the equilibrium in the direction which produces that substance A A + B C + D
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[N2] increases [NH3] increases [H2] decreases
Which way will the equilibrium shift if: [N2] increases [NH3] increases [H2] decreases Answers
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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
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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
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Temperature Changes Increasing temperature will shift the equilibrium in the endothermic direction As heat E is added the system absorbs it
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Which way will equilibrium shift if E in increased?
ΔH = 53.0 kJ
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Decreasing temperature will shift the equilibrium in the exothermic direction
As heat E is decreased the system releases heat E
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Which way will equilibrium shift if temp is decreased?
ΔH = kJ
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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
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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?
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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. )
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Decrease pressure Increase pressure
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LeChatelier’s Principle Practice
Relieve the stress
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THE ↔ END
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