Molar enthalpy of sublimation

T. Kiyobayashi, M. E. Minas da Piedade. The Standard Molar Enthalpy of Sublimation of ry -Bis-pentamethylcyclopentadienyl Iron Measured with an Electrically... 

The molar enthalpy of sublimation A// is rigorously related to the slope dpIdTof the sublimation pressure curve by the Clapeyron equation, which has been discussed in Exp. 13. The exact expression is... 

Ribeiro de Silva, M.A.V., Monte, M.J.S., Huinink, J. (1995) Vapour pressures and standard molar enthalpies of sublimation of seven crystalline copper(ll), P-diketonates. The mean molar (Cu-O) bond-dissociation enthalpies. J. Chem. Thermodyn. 27,175-190. Riddick, J., Bunger, W.B., Sakano, T.K. (1986) Organic Solvents Physical Properties and Method of Purification. 4th Edition, John Wiley Sons, New York. 

Fortunately, the question of aromaticity has been approached experimentally via thermochemical studies in the case of diphenylcyclopropenone " . Careful studies using a rotary-bomb calorimeter as well as a determination of the standard molar enthalpy of sublimation for this compound show that the resonance stabilization in the three-mem bered ring is 18.6 kcalmol" if one assumes a ring strain in cyclopropanone of 67 kcalmol" ... 

Clausius-Clapeyron equation - An approximation to the Clapeyron equation applicable to liquid-gas and solid-gas equilibrium, in which one assumes an ideal gas with volume much greater than the condensed phase volume. For the liquid-gas case, it takes the form d(lnp)/dT = A HIRV- where R is the molar gas constant and A H is the molar enthalpy of vaporization. For the solid-gas case, A H is replaced by the molar enthalpy of sublimation, A H. 

Mis is the molar enthalpy of sublimation (the energy to break all the bonds), Z is the coordination number, and Np, is the Avogadro number. 

Sublimation is the direct conversion of a soUd to a vapor, so the molar enthalpy of sublimation (A//sub) is the energy required to sublime 1 mole of a solid. In general, the molecules in a sohd are more tightly held together by intermolecular forces than those in a liquid, so AHsab is larger than A/fvap- If AHsub. AHyap. and AHfas could all be measured at the same temperature (such as is possible at the triple point of water), we would have... 

The molar enthalpy change A H, of boiling, and, for some elements, the molar enthalpy of sublimation. 

In practice, in the technical Hterature many tables Hst the latent enthalpies of fusion and vaporization of usual compounds, but few data are given regarding the latent enthalpy of sublimation. When such a value is missing, a rule of thumb for assessing the latent enthdpy consists in using the Trouton s first empirical rule, i.e., the latent molar enthalpy of sublimation of a solid corresponds to the sum of its latent molar enthalpies of fusion and of vaporization as follows ... 

Because molecules are more tightly held in a sohd, the vapor pressure of a sohd is generally much less than that of the corresponding liquid. The molar enthalpy of sublimation of a... 

For the liquid phase is very approximately the molar enthalpy of vaporisation, while for solids it is approximately the molar enthalpy of sublimation. Corrections must be applied for the energy of the molecules in the condensed phase and for the work done in expanding the vapour against the atmosphere, so that the best simple approximation to Uq is obtained from the value of extrapolated to absolute zero. For example, the extrapolated value of for liquid argon is about 6400 J mol , and taking 7 as 10 gives a value for Uq of about 21 X 10" J. 

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