Factors Affecting Chemical Equilibrium
🔥 Key NEET Concepts
- Le Chatelier’s Principle applications
- ΔG° = -RT ln K relationship
- Pressure effects on gas equilibria
- Temperature vs. equilibrium constant
- Catalyst role in equilibrium
⚖️ Le Chatelier’s Principle
When equilibrium is disturbed, the system counteracts the change:
- Added reactant? → Reaction consumes it (shifts forward)
- Removed product? → Reaction makes more (shifts forward)
Example for H₂ + I₂ ⇌ 2HI:
Adding H₂ makes \( Q_c = \frac{[HI]^2}{[H_2][I_2]} < K_c \) → Forward shift ✅
🎚️ Concentration Changes
Industrial applications:
- Ammonia synthesis: Remove NH₃(liquid) → Forward shift
- CaO production: CaCO₃(s) → CaO(s) + CO₂(g) → Remove CO₂ → Completes reaction
Experiment: Fe³⁺(aq) + SCN⁻(aq) ⇌ [Fe(SCN)]²⁺(aq) (red)
→ Add oxalic acid: Removes Fe³⁺ → Less red (reverse shift)
→ Add HgCl₂: Removes SCN⁻ → Less red
→ Add KSCN: More SCN⁻ → Deeper red (forward shift) 🔴
📦 Pressure Changes (Gas Reactions Only)
Matters when reactant & product gas moles differ:
- Increase pressure? → Shifts to side with fewer gas moles
- Decrease pressure? → Shifts to side with more gas moles
Example 1: CO(g) + 3H₂(g) ⇌ CH₄(g) + H₂O(g) (4 mol → 2 mol)
↑ Pressure → Forward shift ✅
Example 2: C(s) + CO₂(g) ⇌ 2CO(g) (1 mol → 2 mol)
↑ Pressure → Reverse shift ⬅️
🌡️ Temperature Changes
Changes the equilibrium constant K:
- Exothermic (ΔH < 0): ↑ Temp → ↓ K ← Favors reverse reaction
- Endothermic (ΔH > 0): ↑ Temp → ↑ K ← Favors forward reaction
Experiment 1: 2NO₂(brown) ⇌ N₂O₄(colorless) ΔH = -57.2 kJ/mol
→ Cool (270K): More colorless N₂O₄
→ Heat (363K): More brown NO₂ ☕
Experiment 2: [Co(H₂O)₆]³⁺(pink) + 4Cl⁻ ⇌ [CoCl₄]²⁻(blue) ΔH > 0
→ Cool: Turns pink (reverse shift) 💧
⚡ Effect of Catalyst
Speeds up both forward/reverse reactions equally →
No change in equilibrium position!
Just helps reach equilibrium faster ⏩
Example: Fe catalyst in NH₃ synthesis lets us use moderate temps (500°C)
🔋 Ionic Equilibrium
Solutions with ions conduct electricity → Electrolytes:
- Strong electrolytes: ≈100% ionized (e.g., NaCl → Na⁺ + Cl⁻)
- Weak electrolytes: Partial ionization (e.g., CH₃COOH ⇌ CH₃COO⁻ + H⁺, <5%)
