Energy of sublimation

Typical values of the energy to form vacancies are for silver, lOSkJmol and for aluminium, 65.5kJmol These values should be compared with the values for the activation enthalpy for diffusion which are given in Table 6.2. It can also be seen from the Table 6.2 that die activation enthalpy for selfdiffusion which is related to the energy to break metal-metal bonds and form a vacant site is related semi-quantitatively to the energy of sublimation of the metal, in which process all of the metal atom bonds are broken. 

The lattice energy of a molecular compound corresponds to the energy of sublimation at 0 K. This energy cannot be measured directly, but it is equal to the enthalpy of sublimation at a temperature T plus the thermal energy needed to warm the sample from 0 K to this temperature, minus RT. RT is the amount of energy required to expand one mole of a gas at a temperature T to an infinitely small pressure. These amounts of energy, in principle, can be measured and therefore the lattice energy can be determined experimentally in this case. However, the measurement is not simple and is subject to various uncertainties. 

Following the ideas of Section 2.3, devise a suitable cycle to derive the work function of a metal deposition reaction this will involve the energy of sublimation of the metal. 

Define M/M+ = — AGsub — Im + AGg0l AGsub is the Gibbs energy of sublimation. 

The standard free energy of formation of a gaseous metal ion, AGj (M+, g), can be viewed as the sum of the standard free energy of sublimation, AGj (M , g), and the free energy of ionization, AG j. The standard entropy of a monatomic gas is very nearly equal to the standard entropy of its corresponding monatomic gaseous... 

Standard Enthalpies, Entropies and Gibbs Free Energies of Sublimation of... 

R.B. Cundall et al, "Vapor Pressure Measurements on Some Organic High Explosives , J-ChemSoc, Faraday Trans I, 74 (6), 1339—45 (1978) CA 89, 181933 (1978) [Equilibrium vap press were detd for various expls by the Knudson cell technique. The data for HMX follows the Clausius-Clapeyron eqtn. The values detd for the const A and B in the eqtn, log10p = A—(B/T), plus the std enthalpy, entropy and Gibbs energy of sublimation from the authors calcns are presented in Table 7 ... 

This equation shows that the surface energy per atom correlation between the surface energy per atom and the energy of sublimation (or evaporation) is expected provided mi is constant. Such correlations hold well for the solid and liquid surfaces of metallic bodies and also for the liquid surfaces of oxides and halides (see Figures 4.1,4.9 and 4.10). 

Equation (35) has obvious similarities to Eq. (34). This correspondence can be enhanced by replacing A//sub/RT with Ag sub /RT + 1, which is equivalent since A(pP = RT is an excellent approximation under the conditions of the present experiment. However, Agsub is temperature dependent and refers to the energy of sublimation at the temperature of the experiment rather than at absolute zero. This temperature dependence is reflected in the statistical treatment by the variation with T of the second term on the left-hand side (LHS) of Eq. (34). 

The energy of sublimation for lithium is 155.2 kJ/mol. Dissociate mole of F2 gas into separate gaseous F Atoms ... 

The major component of AG° is the lattice energy of the solid which is nearly always greater than 400 kJ/mole, so if the free energy of solution is to be negative, powerful forces must hold the ions and solvent molecules together. The free energy of sublimation of the lattice is given by Eqn. 61 and, for uni-univalent salts by Eqn. 

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