Definition
The quantity of heat absorbed or released by a substance when it changes physical state (solid to liquid, liquid to vapor, or the reverse) without any change in its temperature. The heat energy goes into breaking or forming the bonds between molecules rather than raising or lowering the temperature reading.
Plain English
Heat that goes into changing something from solid to liquid, or liquid to gas (or back again), without making it any hotter or colder. The thermometer doesn't move while this is happening, but heat is still flowing in or out.
Context Anchor
Seen in aircraft environmental systems, refrigeration and air-conditioning discussions, and weather topics involving water vapor, clouds, and icing.
Derivation
From the Latin 'latens', meaning hidden or concealed. The heat is 'hidden' because it is being absorbed or released without showing up on a thermometer.
Why Pilots Care
Drives thunderstorm development and influences icing and aircraft performance calculations.
Analogy
When a pot of water is boiling, adding more heat does not make the boiling water much hotter; much of that energy goes into turning the water into steam. That energy is latent heat.
Grounding Statement
Picture a pot of boiling water on a stove. Even with the burner on full, the water stays at 212°F until it has all boiled away. The heat going in isn't raising the temperature — it's turning liquid into vapor. That energy is the latent heat.
Intuition Check
Latent does not mean “late.” Here it means hidden: heat is moving in or out, but the temperature may stay the same while the substance changes form.
Example Sentence 1
The air conditioning system cools the cabin by using the latent heat absorbed when the refrigerant evaporates inside the evaporator coil.
Example Sentence 2
Mechanics account for latent heat when evaluating cooling effects on aircraft surfaces.