![]() ![]() The Born-Haber cycle for the sodium chloride molecular consists of the thermodynamic cycle shown in Figure 1 and with the enthalpy values of the reactions listed in Table I. The value of is derived from enthalpy data through the Born-Haber thermodynamic cycle. It is highly exothermic and therefore the enthalpy value is negative. The opposite reaction or the formation of the crystal The dissociation of the crystal lattice is endothermic, therefore the values of $ latex $ are always positive. The enthalpy of dissociation of the crystal lattice (or reticular enthalpy,, where stand for crystal) is the standard enthalpy variation that accompanies the formation of an ion gas starting from the corresponding ionic solid: The reticular energetic can therefore be discussed solely on the basis of the lattice enthalpy. The lattice formation process starting from an ion in gas phase is so exothermic that at room temperature (298 K) the entropic contribution can be neglected (the entropic effect due to temperature becomes completely negligible only at temperatures close to absolute zero, ). If is more negative for the formation of the structure than for the structure, the transition will be spontaneous and the solid will have that structure. ![]() The stability of a crystal lattice at constant T and P conditions is linked to the Gibbs free energy of lattice formation by the relations ![]() My blog in italian on this topics is very popular and for this reason I decided to add an English translation (when I have some free time, I will also translate the text in the Figure and Table). ![]()
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