Key facts & rules

• Reversible reaction: can proceed in both directions (shown with ⇌).
• Dynamic equilibrium: forward rate = backward rate; concentrations constant (but not necessarily equal).
• Le Chatelier's principle: if a system at equilibrium is disturbed, it shifts to oppose the change.
• Temperature ↑: equilibrium shifts to endothermic direction (reduces temperature).
• Pressure ↑: equilibrium shifts to side with fewer moles of gas.
• Concentration ↑ of a reactant: equilibrium shifts to right (makes more products).
• Haber process: N₂ + 3H₂ ⇌ 2NH₃ (ΔH = −92 kJ/mol). Conditions: 450°C, 200 atm, iron catalyst.
• Contact process (H₂SO₄): 2SO₂ + O₂ ⇌ 2SO₃. Conditions: 450°C, 1–2 atm, V₂O₅ catalyst.