is the quantity of heat absorbed or released by a substance undergoing a change of state (e.g., ice changing to liquid water, or water to steam) without change of temperature. At standard atmospheric pressure, the latent heat of vaporization of water is 2256 kJ/kg (970 Btu/lb); this is the amount of energy required to convert water at 100°C (212°F) to steam at the same temperature. Conversely, when steam condenses at 100°C, the same amount of heat is released.