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Enthalpies of melting and boiling for pure elements versus temperatures of transition, demonstrating Trouton's rule. In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure.
Black next showed that a water temperature of 176 °F was needed to melt an equal mass of ice until it was all 32 °F. So now 176 – 32 = 144 “degrees of heat” seemed to be needed to melt the ice. The modern value for the heat of fusion of ice would be 143 “degrees of heat” on the same scale (79.5 “degrees of heat Celsius”). [18] [15]
The heat content of an ideal gas is independent of pressure (or volume), but the heat content of real gases varies with pressure, hence the need to define the state for the gas (real or ideal) and the pressure. Note that for some thermodynamic databases such as for steam, the reference temperature is 273.15 K (0 °C).
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 specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher.
Through the procedure called ebullioscopy, a known constant can be used to calculate an unknown molar mass. The term ebullioscopy means "boiling measurement" in Latin . This is related to cryoscopy , which determines the same value from the cryoscopic constant (of freezing point depression ).
In the above equation, T F is the normal freezing point of the pure solvent (273 K for water, for example); a liq is the activity of the solvent in the solution (water activity for aqueous solution); ΔH fus T F is the enthalpy change of fusion of the pure solvent at T F, which is 333.6 J/g for water at 273 K; ΔC fus p is the difference ...
Specifically, at constant atmospheric pressure, in a system containing C linearly independent chemical components, if C +1 phases are specified to be present in equilibrium, then the system is fully determined (there are no degrees of freedom). That is, the temperature and the compositions of all phases are determined.