The amount of energy needed to change phase is called latent heat. The latent heat involved in the transition from solid to liquid is called the latent heat of fusion while the energy involved in the transition from liquid to gas is called the latent heat of vaporization. For water the latent heat of fusion is 334 kJ/kg. The latent heat of vaporization is 2,265 kJ/kg.

Energy must be added to go from ice to water and water to steam, but if steam condenses to water it produces 2,265 kJ for each kilogram of steam condensed. That’s the reason that steam burns are so dangerous. Almost all of that energy is transferred to your skin. If water freezes it releases 334 kJ for each kilogram of water frozen. In a freezer that amount of energy must be removed by the freezing mechanism.