Evaporation Heats of Compounds

As mentioned above, the evaporation heat can be calculated as the difference between the sublimation heat and the melting heat. A survey of direct measurements of AH from 1910 to 2010 is available [85] extracts from it are presented in Table 9.7, together with data from the reference book [45] and papers [86]. A comparison with Table 9.6 reveals that AHy are close to AH for various substances. 

Evaporation heats of organic compounds are additive properties, i.e. can be expressed through the sum of increments corresponding to individual atoms, chemical bonds and/or radicals. Thus, Korolev et al. [87] derived the formula AHy (kJ/mol) = A//vx-l-A//vch [85], where AT/yx and AHvch are the increments of 

Vaporization enthalpy appears to be a linear function of the number of carbon atoms not only for alkanes or nitriles but also for alkyl-azides. The dependence of vaporization enthalpy (in kJ/mol) on the number of carbon atoms (Nc = 4-10) for mono-azides CH3—(CH2)n N3 obeys the equation AH —16.6-1-5.8 Nc. The dependence of vaporization enthalpy on the number of carbon atoms for di-azides N3 (CH2)n—N3 with n = (3 to 6) is described by the equation A Wv = 33.3-1-6.6 Vc [89]. 

Class Group a Class Group a Class Group a 

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