Sublimation is the phase transition in which a solid changes directly into a gas without passing through the liquid state.
This process requires energy to overcome the intermolecular forces holding the particles in the solid lattice so that they can escape into the gas phase. Since energy must be supplied to the substance, sublimation is an endothermic process, meaning it involves energy absorption.
The other options are incorrect:
Vapourization refers specifically to the change from liquid to gas (boiling or evaporation), not from solid to gas.
Melting is the change from solid to liquid, not solid to gas.
Osmotic diffusion refers to the movement of solvent molecules through a semipermeable membrane, which is unrelated to phase changes.
Exam tip: Common examples of sublimation include solid carbon dioxide (dry ice) turning directly into CO2 gas, iodine crystals forming purple vapour when heated, and solid naphthalene (mothballs) gradually disappearing into vapour.
