Materials change state all the time, but how and why? Material processes - Solids, liquids and gases - Changes of state Learning Points Melting is the change of state from solid to liquid. Evaporation is the change of state from liquid to gas. Liquid water turns to steam at 100°C. A Twig Curriculum Film. Delivering key learning points. Get straight to the facts in just three minutes – directly linked to core learning, Twig's curriculum films will fit neatly into your lesson plans.