3.4 - Reversible Reactions & Equilibrium

Reversible reactions

• In a reversible reaction, the products can react together to re-form the original reactants, so the reaction can run in either direction.
• A reversible reaction is written with the ⇌ symbol in place of the usual arrow:
  • A + B ⇌ C + D

The direction a reversible reaction runs in, and how far it goes, depends on the conditions (such as temperature, pressure, and concentration).

Example - Heating ammonium chloride

• Heating white solid ammonium chloride breaks it down into ammonia and hydrogen chloride (both colourless gases).
• Cooling the gases lets them recombine into solid ammonium chloride again.
• Ammonium chloride ⇌ ammonia + hydrogen chloride