It is possible to calculate a theoretical value of the lattice energy for a molecular crystal if data are available on the potential energy between atoms as a frmction of their separation. A commonly used form for the interatomic potential (see Fig. 1) is due to Lennard-Jones " [Pg.518]

Quite apart from its theoretical calculation, by the use of one of the expressions developed above, it is possible to relate the lattice energy of an ionic crystal to various measurable thermodynamic quantities by means of a simple Hess s law cycle. This cycle was first proposed and used by Bom 15) and represented in its familiar graphical form by Haber (45). It is now usually referred to as the Born-Haber cycle. The cycle is given below for a uni-univalent salt in terms of enthalpies. [Pg.160]

Finally, use Eq. (8) to determine the experimental value of the lattice energy of argon at 0 K. X-ray diffraction data give 5.30 A for the cubic unit-cell parameter of solid argon at 4 K. Find the nearest-neighbor distance d, and use Eqs. (10) and (11) to calculate a theoreticaf value of

It must be remembered that the lattice energy given by the Bom-Haber cycle is an experimental lattice energy and is not,dependent upon the nature of the assumptions made about the bonding in the crystal. The classical theoretical calculations are of course dependent upon the assumption of the ionic nature of the bonding in the lattice. Because of this the Bom-Haber cycle has been used mainly for three purposes. [Pg.161]

Self-consistent energy band calculations have now been made through the LMTO method for all of the NaCl-type actinide pnictides and chalcogenides . The equation of state is derived quite naturally from these calculations through the pressure formula extended to the case of compounds . The theoretical lattice parameter is then given by the condition of zero pressure. [Pg.283]

It is important to note that the theoretical results obtained by Flory about the dependence of the critical concentrations v and vj on x are in good agreement with experimental data. It is sufficient to remember, as an example, the results obtained by Flory for PBLG solutions in dioxane (Fig. 4). The discrepancy between the experimental results (solid curves) and theoretical calculations (dashed curves) looks quite natural on the account of a number of assumptions made when deriving the equation for the free energy on the basis of the lattice model (see also ). [Pg.84]

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