What is a reversible reaction? — A reaction that can proceed in both the forward and reverse directions. Shown by the double arrow (⇌). Example: N₂ + 3H₂ ⇌ 2NH₃. Products can react to reform reactants.

What is dynamic equilibrium? — The state in a reversible reaction where the forward reaction rate equals the reverse reaction rate. Concentrations of reactants and products remain constant — but both reactions are still occurring simultaneously.

What are the conditions needed for equilibrium to be established? — The system must be closed (no substances can enter or leave). The reaction must be reversible. Equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction.

What is the equilibrium constant Kc? — For the reaction aA + bB ⇌ cC + dD: Kc = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ where [ ] = molar concentrations at equilibrium. Kc is constant at a given temperature. Pure solids and liquids are excluded.

What does the magnitude of Kc tell you? — Kc >> 1: Equilibrium lies to the right — products favoured. Kc << 1: Equilibrium lies to the left — reactants favoured. Kc ≈ 1: Significant amounts of both reactants and products present.

What is Kp and how does it differ from Kc? — Kp is the equilibrium constant expressed in terms of partial pressures of gases (in atm or Pa). Used for gas-phase reactions. Related to Kc by: Kp = Kc(RT)^Δn where Δn = moles of gaseous products − moles of gaseous reactants.

What is the reaction quotient Q? — Q has the same expression as Kc but uses current concentrations (not equilibrium). Q < Kc: Reaction proceeds forward (more products form). Q > Kc: Reaction proceeds backward. Q = Kc: System is at equilibrium.

What is Le Chatelier's Principle? — "If a system at equilibrium is subjected to a change (stress), the system will shift its equilibrium position in the direction that partially counteracts the applied change." — Henri Louis Le Chatelier (1884).

How does increasing concentration of a reactant affect equilibrium? — The system shifts to the right (forward reaction) to use up the added reactant and partially reduce the disturbance. More products are formed. Kc itself does not change (temperature is constant).

How does increasing pressure affect equilibrium? — The system shifts toward the side with fewer moles of gas to reduce the pressure. Example: N₂ + 3H₂ ⇌ 2NH₃ (4 mol gas → 2 mol gas) — increased pressure shifts equilibrium right. No effect if Δn = 0.

How does increasing temperature affect equilibrium? — The system shifts in the endothermic direction (absorbs heat) to counteract the increase. This is the only change that alters the value of Kc. Exothermic reactions: Kc decreases. Endothermic reactions: Kc increases.

How does a catalyst affect equilibrium? — A catalyst increases the rates of both forward and reverse reactions equally — it does NOT shift the equilibrium position and does NOT change Kc. It only helps the system reach equilibrium faster.

What is the Haber Process and what conditions are used? — Industrial synthesis of ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ/mol. Conditions: Temperature ~450°C (compromise), Pressure ~200 atm, Iron catalyst. High pressure favours NH₃ (fewer gas moles); low temperature favours NH₃ (exothermic) but slows reaction.

Why is the Haber Process temperature a compromise? — Low temperature gives higher yield (exothermic reaction — Le Chatelier) but the rate is too slow to be economical. High temperature gives faster rate but lower equilibrium yield. ~450°C gives acceptable rate and reasonable yield.

What is the Contact Process? — Industrial production of sulfuric acid (H₂SO₄). Key equilibrium step: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −196 kJ/mol. Conditions: 450°C, 1–2 atm, V₂O₅ catalyst. SO₃ then reacts with H₂SO₄ to form oleum, then diluted with water.

What is an homogeneous equilibrium? — All reactants and products are in the same phase (e.g., all gases or all in aqueous solution). Example: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) — all gases.

What is a heterogeneous equilibrium? — Reactants and products are in different phases. Pure solids and liquids are excluded from the Kc expression (their concentrations are constant). Example: CaCO₃(s) ⇌ CaO(s) + CO₂(g) — Kc = [CO₂] only.

How does adding an inert gas at constant volume affect equilibrium? — It does NOT affect the equilibrium. The partial pressures and concentrations of reacting gases are unchanged. The total pressure increases but the equilibrium position stays the same.

What is the solubility product (Ksp)? — The equilibrium constant for the dissolution of a sparingly soluble ionic compound. For AB(s) ⇌ A⁺(aq) + B⁻(aq): Ksp = [A⁺][B⁻]. Small Ksp = very insoluble. Used to predict whether a precipitate will form.

What is the common ion effect? — The reduction in solubility of an ionic compound when a solution already contains one of its ions. Adding a common ion shifts equilibrium to the left (Le Chatelier) — less compound dissolves. Used in buffer solutions and qualitative analysis.

What is a strong electrolyte vs a weak electrolyte? — Strong electrolyte: Completely dissociates in water (strong acids, strong bases, most salts). Kc is very large. Weak electrolyte: Partially dissociates — establishes equilibrium (weak acids, weak bases). Kc is small.

What effect does decreasing pressure have on a gaseous equilibrium? — The system shifts toward the side with more moles of gas to increase pressure. The opposite of increasing pressure. For the Haber Process, decreasing pressure shifts equilibrium left — less NH₃ produced.

What is the Ostwald Dilution Law? — For a weak acid HA ⇌ H⁺ + A⁻ with Ka: the degree of dissociation α ≈ √(Ka/C) at low concentrations. As concentration C decreases, the degree of dissociation increases — dilution favours ionization (Le Chatelier).

How does temperature affect Kc for an exothermic reaction? — Heat can be treated as a product: A + B ⇌ C + D + heat. Increasing temperature adds heat (product) → equilibrium shifts LEFT → fewer products → Kc decreases. Cooling increases Kc for exothermic reactions.

What is the relationship between ΔG° and Kc? — ΔG° = −RT ln Kc. If Kc > 1: ΔG° < 0 (products favoured). If Kc < 1: ΔG° > 0 (reactants favoured). This links thermodynamics and equilibrium — the equilibrium constant is a thermodynamic quantity.