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The enthalpy of vaporization is a function of the pressure and temperature at which the transformation (vaporization or evaporation) takes place. The enthalpy of vaporization is often quoted for the normal boiling temperature of the substance. Although tabulated values are usually corrected to 298 K, that correction is often smaller than the ...
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid [ 1 ][ 2 ] and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum, i.e., under a lower pressure, has a lower ...
Melting-point apparatus. A Fisher–Johns apparatus. A melting-point apparatus is a scientific instrument used to determine the melting point of a substance. Some types of melting-point apparatuses include the Thiele tube, Fisher-Johns apparatus, Gallenkamp (Electronic) melting-point apparatus and automatic melting-point apparatus.
Boiling-point elevation. Boiling-point elevation is the phenomenon whereby the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.
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). This property of elevation of boiling point is a ...
Boiling-point diagram. The preceding equilibrium equations are typically applied for each phase (liquid or vapor) individually, but the result can be plotted in a single diagram. In a binary boiling-point diagram, temperature (T ) (or sometimes pressure) is graphed vs. x 1. At any given temperature (or pressure) where both phases are present ...
The standard molar entropy at pressure = is usually given the symbol S°, and has units of joules per mole per kelvin (J⋅mol −1 ⋅K −1). Unlike standard enthalpies of formation, the value of S° is absolute. That is, an element in its standard state has a definite, nonzero value of S at room temperature. The entropy of a pure crystalline ...
Antoine equation. The Antoine equation is a class of semi-empirical correlations describing the relation between vapor pressure and temperature for pure substances. The Antoine equation is derived from the Clausius–Clapeyron relation. The equation was presented in 1888 by the French engineer Louis Charles Antoine [fr] (1825–1897).