Equilibrium Constant and Le Chatelier's Principle
At equilibrium the forward and reverse rates are equal and the equilibrium constant K is fixed at a given temperature; the system shifts to oppose an imposed change.
What is Equilibrium Constant and Le Chatelier's Principle?
At equilibrium the forward and reverse rates are equal and the equilibrium constant K is fixed at a given temperature; the system shifts to oppose an imposed change.
Key formula / rule: Kp = Kc (RT)dn for gaseous equilibria.
Key points
- Compute the equilibrium constant from equilibrium concentrations.
- Predict the direction of shift for an imposed change.
Common exam trap
Claiming a catalyst shifts the equilibrium position.
Definitions
- Term
Equilibrium Constant and Le Chatelier's Principle
- Meaning
At equilibrium the forward and reverse rates are equal and the equilibrium constant K is fixed at a given temperature; the system shifts to oppose an imposed change.
- Term
Equilibrium Constant and Le Chatelier's Principle — explanation
- Meaning
K depends only on temperature, so pressure and concentration changes shift the position of equilibrium without changing K. Comparing the reaction quotient Q with K predicts the direction of shift.
Learning objectives
Compute the equilibrium constant from equilibrium concentrations.
Predict the direction of shift for an imposed change.
Formulae
- Key point
Kp = Kc (RT)dn for gaseous equilibria.
- Key point
Q < K shifts the reaction forward; Q > K shifts it backward.
- Key point
Only temperature changes the value of K.
Prerequisites
CHE-U1-TH-T2-S1-C3
Common mistakes
Claiming a catalyst shifts the equilibrium position.
Including pure solids and liquids in the equilibrium expression.
Keywords
Equilibrium
Constant
Chatelier's
Principle
Practice preview
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For the reaction N2(g) + 3H2(g) <=> 2NH3(g), which is exothermic (Delta H = -92.4 kJ/mol), which set of conditions would maximize the yield of ammonia?…
hard