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Enthalpy (/ ˈ ɛ n θ əl p i / ⓘ) is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. [1] It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant external pressure, which is conveniently provided by the large ambient atmosphere.
The dimensionless humidity ratio is typically expressed as grams of water per kilogram of dry air, or grains of water per pound of air (7000 grains equal 1 pound). Specific enthalpy, symbolized by h, is the sum of the internal (heat) energy of the moist air in question, including the heat of the air and water vapor within. Also called heat ...
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.
The August equation describes a linear relation between the logarithm of the pressure and the reciprocal temp. This assumes a temperature-independent heat of vaporization. The Antoine equation allows an improved, but still inexact description of the change of the heat of vaporization with the temperature.
The energy needed to do that has been taken from the air. Taking a volume of air at temperature T and mixing ratio of r , drying it by condensation will restore energy to the airmass. This will depend on the latent heat release as: T e ≈ T + L v c p d r {\displaystyle T_{e}\approx T+{\frac {L_{v}}{c_{pd}}}r} where:
The Mollier enthalpy–entropy diagram for water and steam. The "dryness fraction", x , gives the fraction by mass of gaseous water in the wet region, the remainder being droplets of liquid. An enthalpy–entropy chart , also known as the H – S chart or Mollier diagram , plots the total heat against entropy, [ 1 ] describing the enthalpy of a ...
Water vapor and dry air density calculations at 0 °C: The molar mass of water is 18.02 g/mol , as calculated from the sum of the atomic masses of its constituent atoms . The average molar mass of air (approx. 78% nitrogen, N 2 ; 21% oxygen, O 2 ; 1% other gases) is 28.57 g/mol at standard temperature and pressure ( STP ).
A formula to compute the ebullioscopic constant is: [2] = R is the ideal gas constant. M is the molar mass of the solvent. T b is boiling point of the pure solvent in kelvin. ΔH vap is the molar enthalpy of vaporization of the solvent.