Summary
Chemical equilibria involve the balance between reactants and products in a reversible reaction, where the rates of the forward and reverse reactions are equal.
- Equilibrium Constant (Kc) — a measure of the position of equilibrium in a chemical reaction. Example: In the reaction A + B ⇌ C + D, Kc = [C][D]/[A][B].
- Partial Pressure — the pressure exerted by a single gas in a mixture of gases. Example: In a mixture of gases, the partial pressure of oxygen can be calculated using its mole fraction and the total pressure.
- Mole Fraction — the ratio of the number of moles of a component to the total number of moles in a mixture. Example: In a mixture of 2 moles of hydrogen and 3 moles of oxygen, the mole fraction of hydrogen is 2/5.
- Gibbs Free Energy (G) — the energy associated with a chemical reaction that can be used to do work. Example: If ΔG < 0, the reaction is spontaneous.
Exam Tips
Key Definitions to Remember
- Equilibrium Constant (Kc)
- Partial Pressure
- Mole Fraction
- Gibbs Free Energy (G)
Common Confusions
- Confusing Kc with reaction rate
- Misunderstanding the significance of ΔG being zero
Typical Exam Questions
- What is the equilibrium constant for a given reaction? Calculate using concentrations of products and reactants.
- How do you calculate the partial pressure of a gas in a mixture? Use the mole fraction and total pressure.
- What does a negative ΔG indicate about a reaction? It indicates the reaction is spontaneous.
What Examiners Usually Test
- Understanding of how to calculate and interpret Kc and Kp
- Ability to apply the Gibbs equation to determine reaction feasibility
- Effects of temperature changes on equilibrium and reaction spontaneity