Born-Haber cycle solubility

The initiation of the cationic polymerisation of alkenes is examined in detail by means of simple thermodynamic concepts. From a consideration of the kinetic requirements it is shown that the ideal initiator will yield a stable, singly charged anion and a cation with a high reactivity towards the monomer by simple, well defined reactions. It must also be adequately soluble in the solvent of choice and for the experimental method to be used. The calculations are applied to carbocation salts as initiators and a method of predicting their relative solubilities is described. From established and predicted data for a variety of carbocation salts the position of their ion molecule equilibria and their reactivity towards alkenes are examined by means of Born-Haber cycles. This treatment established the relative stabilities of a number of anions and the reason for dityl, but not trityl salts initiating the polymerisation of isobutene. 

Solubility equilibria can be treated in terms of the free energy of solution, as outlined in Section 2.3, and the temperature dependences can be related to the enthalpy and entropy of solution. The Born-Haber cycle for solutions, in terms of enthalpies, can be written as follows ... 

The formation of ionic crystals is calculated using the Born-Haber cycle. It s called a cycle because ultimately the compound can cycle back and forth between its crystal form and its free ion form. When you go on a road trip, you want to be able to go home when you re done traveling. Just as the atoms can break apart and become soluble in an appropriate solvent, they can recombine (aggregate) to form a solid again under the appropriate conditions. Lattice energy plays a major role in the formation of ionic crystals. 

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