Heat of vapourisation

Lag in the system 509 Langmuir-Hinshelwood kinetics 321 Laplace transformation 80, 536 Latent heat of vapourisation 517 Least squares 112 Level control 509... 

For ionic crystals > = 1, and the A are known (Madelung constants). For van der Waals crystals m — 6 (though small terms in and exist) but in view of the difficulties of calculation we obtain B from the observed heat of vapourisation (from A. 3). The repulsion exponent n varies from about 6 for LiF to 12 for Csl, for gases (Lennard-Jones) a value of about 12 seems the best. We assume a constant value of 11 throughout. 

According to the most recent measurements the critical pressure is 65 at and the critical temperature 52 °C Earlier work gave similar values 273,281) jjjg latent heat of vapourisation of phosphine at the boiling point was... 

DH, DS and DGfor the vapourisation of 2 moles of benzene at its boiling point (80.2°C) calculated. Latent heat of vapourisation = 101 cals, gnu-i ... 

For latent heat, we look up the corresponding entry in the tables for either the latent heat of vapourisation (or simply the heat of vapourisation) or the heat of fusion, depending on the type of phase change encountered (liquid to vapour and solid to liquid, respectively). These quantities are in units of energy per unit mass and are given for a specific reference state (often the 1 atm boiling point or melting point of the substance). 

Table 2 Data for calculation of enthalpies for sensible heat and the latent heat of vapourisation...

Although reverse osmosis can be used to separate organic and aqueous-organic liquid mixtures, very high pressures are required. Alternatively, pervaporation can be used in which the species being absorbed by, and transported through, the non-porous membrane are evaporated. This method, which uses much lower pressures than reverse osmosis, but where the heat of vapourisation must be supplied, is used to separate azeotropic mixtures. 

Given the heat of vapourisation of the mixture, the required heat input gR (in kW) can be found from the vapour flow rate V. In the calculations above, the reflux ratio was given. As mentioned earlier, different values are typically considered, and the calculations repeated, to determine the reflux ratio which gives the most economical column operation and design. 

H ) heat of vapourisation. The change in enthalpy when one mole of liquid evaporates to form one mole of gas. Enthalpies of vapourisation are always positive because vapourisation involves overcoming most of the intermolecular attractions in the liquid. 

The vapour enthalpies are calculated from the molar heat capacity functions for the vapour components and the latent heats of vapourisation at standard... 

The above interaction parameters may be related to the Hildebrand solubility parameter [22] 8 (at the oil side of the interface) and the Hansen [23] nonpolar, hydrogen-bonding and polar contributions to 8 at the water side of the interface. The solubility parameter of any component is related to its heat of vapourisation AH by the expression. 

The Hildebrand solubility parameter S is defined as the square root of the cohesive energy density (the cohesive energy density is the amount of energy needed to completely remove a unit volume of molecules from their neighbours to infinite separation). This is equal to the heat of vapourisation of the compound divided by its volume in the condensed phase and is given by ... 

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