Study Notes
In chemistry, equilibrium refers to the state where the rates of the forward and backward reactions are equal, resulting in constant concentrations of reactants and products.
- Le Châtelier's Principle — if a change is made to a system at dynamic equilibrium, the position of the equilibrium moves to minimize this change. Example: Increasing the concentration of a reactant shifts the equilibrium to the right.
- Equilibrium Constant (Kc) — a value that expresses the ratio of concentrations of products to reactants at equilibrium. Example: For the reaction aA + bB ⇌ cC + dD, Kc = [C]^c[D]^d / [A]^a[B]^b.
- Gibbs Free Energy (ΔG) — relates to the spontaneity of a reaction and its equilibrium constant. Example: ΔG = -RT lnK, where a negative ΔG indicates a spontaneous reaction.
Exam Tips
Key Definitions to Remember
- Le Châtelier's Principle
- Equilibrium Constant (Kc)
- Gibbs Free Energy (ΔG)
Common Confusions
- Assuming Kc changes with concentration changes
- Misunderstanding the effect of temperature on Kc
Typical Exam Questions
- What happens to the equilibrium position when the concentration of a reactant is increased? The equilibrium shifts to the right.
- How does a negative ΔG relate to equilibrium? It indicates the reaction is spontaneous and products are favored.
- What is the effect of temperature on Kc? Only temperature changes affect Kc.
What Examiners Usually Test
- Application of Le Châtelier's Principle
- Calculations involving Kc
- Relationship between ΔG and Kc