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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.
Enthalpies of melting and boiling for pure elements versus temperatures of transition, demonstrating Trouton's rule. In thermodynamics, Trouton's rule states that the (molar) entropy of vaporization is almost the same value, about 10.5 in nondimesnional units, or 85–88 if expressed in units J/(K·mol), for various kinds of liquids at their boiling points. [1]
Latent heat is associated with the change of phase of atmospheric or ocean water, vaporization, condensation, freezing or melting, whereas sensible heat is energy transferred that is evident in change of the temperature of the atmosphere or ocean, or ice, without those phase changes, though it is associated with changes of pressure and volume.
Water has a very high specific heat capacity of 4184 J/(kg·K) at 20 °C (4182 J/(kg·K) at 25 °C)—the second-highest among all the heteroatomic species (after ammonia), as well as a high heat of vaporization (40.65 kJ/mol or 2268 kJ/kg at the normal boiling point), both of which are a result of the extensive hydrogen bonding between its ...
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.
λ v = Latent heat of vaporization. The energy required per unit mass of water vaporized. (J g −1) L v = Volumetric latent heat of vaporization. The energy required per unit volume of water vaporized. (L v = 2453 MJ m −3) E = Mass water evapotranspiration rate (g s −1 m −2) ET = Water volume evapotranspired (mm s −1)
λ v = latent heat of vaporization (J kg −1) γ = psychrometric constant (Pa K −1) which (if the SI units in parentheses are used) will give the evaporation E mass in units of kg/(m 2 ·s), kilograms of water evaporated every second for each square meter of area. Remove λ to obviate that this is fundamentally an energy balance.
= latent heat of water vaporization, 2.45 [MJ kg −1], = specific heat of air at constant pressure, [MJ kg −1 °C −1], = ratio molecular weight of water vapor/dry air = 0.622. Both and are constants.