Latent Heat
Latent heat is the energy absorbed or released when a substance changes phase — such as water boiling to steam — at constant temperature. It is large compared with sensible heat and underpins the usefulness of steam as an energy carrier.
During a phase change, added energy goes into breaking molecular bonds rather than raising temperature, so a thermometer reads steady while the change occurs. Water's latent heat of vaporisation is far greater than the sensible heat needed to warm it to boiling, which is why steam can deliver so much heat as it condenses on a process surface. Recovering this latent heat through condensate return and condensing economisers is a major efficiency opportunity.