Enthalpy of vapourization

Fig. 3.2 shows the case of a jacketed, stirred-tank reactor, in which either heating by steam or cooling medium can be applied to the jacket. Here V is volume, Cp is specific heat capacity, p is density, Q is the rate of heat transfer, U is the overall heat transfer coefficient, A is the area for heat transfer, T is temperature, H is enthalpy of vapour, h is liquid enthalpy, F is volumetric flow... 

The enthalpies of vapourization of interest found in Reference 16 and Reference 21 vary no more than 0.1 kJ mol-1, except for the values for cis-2-hexene which differ by 0.7 kJ mol-1. We chose AHy = 32.2 kJ mol-1 from the latter source. 

Our further analysis of the enthalpy of formation of 2-methylbicyclo[2.2.1]heptene only worsens the disparity. That is, we find methylation of one doubly bonded carbon in gaseous cyclopropene, cyclopentene and cyclohexene is accompanied by a decrease in enthalpy of formation of 34, 38 and 38 kJmol-1, i.e. 36 2 kJmol-1. The recommended enthalpy of formation of bicyclo[2.2.1]heptene (see Reference 60) is 90 kJmol-1 and so we would predict an enthalpy of formation of its gaseous 2-methyl derivative of 90 — 36 54 kJmol-1. Using our standard enthalpy of vapourization estimation protocol we would predict a phase-change enthalpy of 40 kJmol-1 for this species, and so derive an enthalpy of formation of liquid 2-methylbicyclo[2.2.1]heptene of ca 54-40 15 kJmol-1. That is, if anything, the exocyclic species is too stable if we compare this derived value with 4.5 1.8 kJmol-1 derived from the available combustion calorimetric data. 

We recall die use of die substituent constants for die relevant >CO and X groups from the preceding reference for generating near-additivity for enthalpies of vapourization of many other types of —COX species, J. F. Liebman and J. S. Chickos, Struct. Chem., 1, 501 (1990). 

Since the enthalpy of vapourization for NG and the lattice enthalpy for ADN are known, the gas-phase enthalpy values can easily be converted into the standard enthalpies of formation for the condensed phase ... 

In addition to Trouton s rule, some other parameters for measuring the structuredness of solvents have been recommended, for example a solvent dipole orientation correlation parameter [175, 200], the solvent s heat capacity density [175, 200], and a so-called Ap parameter derived from the solvent s enthalpy of vapourization minus EPD/ EPA and van der Waals interactions [201], According to these parameters, solvents can be classified as highly structured e.g. water, formamide), weakly structured e.g. DMSO, DMF), and practically non-structured e.g. -hexane and other hydrocarbons) [200, 201]. 

The thermophysical and thermodynamic properties of liquid water as well as its chemical properties, all depend on the temperature and the pressure. The thermophysical and thermodynamic properties include the density p, the molar volume V = M/p, the isothermal compressibility/ct = P (dp/d P)t = —V (dV/dP)T, the isobaric expansibility ap = —p dp/dT)p = V dV/dT)p, the saturation vapour pressure p, the molar enthalpy of vapourization Ayf7, the isobaric molar heat capacity Cp, the Hildebrand solubility parameter 3h = [(Ay// —RT)/ the surface tension y, the dynamic viscosity rj, the relative permittivity Sr, the refractive index (at the sodium D-line) and the self-diffusion coefficient T>. These are shown... 

The work that must be expended in order to create a cavity in a liquid measures its stiffness. Such a cavity is required in order to accommodate a molecule of the liquid itself, condensing into it from the vapour, or of a solute particle. This work per unit volume of the cavity can be obtained from the thermodynamic quantities characterizing the liquid its molar enthalpy of vapourization AyH, its molar volume V, its isobaric expansibility ap, its isothermal compressibility kj, and its vapour pressure pc, all at the temperature of interest T. These yield the difference between the cohesive energy density ced = = [AyH — RT]/V and the internal pressure... 

In addition, because of its low enthalpy of vapourization, Zn allows good heat transfer by condensation and finally Zn has a hypergoHc effect on the molten TNT [16]. 

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