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Temperature-dependency of the heats of vaporization for water, methanol, benzene, and acetone. In thermodynamics, the enthalpy of vaporization (symbol ∆H vap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas.
Latent heat is energy released or absorbed by a body or a thermodynamic system during a constant-temperature process. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.
However, the liquid–vapor boundary terminates in an endpoint at some critical temperature T c and critical pressure p c. This is the critical point . The critical point of water occurs at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm; 220.64 bar).
For a liquid–gas transition, is the molar latent heat (or molar enthalpy) of vaporization; for a solid–gas transition, is the molar latent heat of sublimation. If the latent heat is known, then knowledge of one point on the coexistence curve , for instance (1 bar, 373 K) for water, determines the rest of the curve.
To convert heat values to joules per mole values, multiply by 44.095 g/mol. To convert densities to moles per liter, multiply by 22.678 cm 3 mol/(L·g). Data obtained from CRC Handbook of Chemistry and Physics , 44th ed. pages 2560–2561, except for critical temperature line (31.1 °C) and temperatures −30 °C and below, which are taken from ...
L is the latent heat of vaporization at the temperature T, T C is the critical temperature, L 0 is the parameter that is equal to the heat of vaporization at zero temperature (T → 0), tanh is the hyperbolic tangent function. This equation was obtained in 1955 by Yu. I. Shimansky, at first empirically, and later derived theoretically.
Graph of temperature of phases of water heated from −100 °C to 200 °C – the dashed line example shows that melting and heating 1 kg of ice at −50 °C to water at 40 °C needs 600 kJ The specific heat capacities of gases can be measured at constant volume, by enclosing the sample in a rigid container.
For example, latent heat release in atmospheric convection is directly responsible for powering destructive storms such as tropical cyclones and severe thunderstorms. Water vapor is an important greenhouse gas [18] [19] owing to the presence of the hydroxyl bond which strongly absorbs in the infra-red.