Thermodynamic arguments in inorganic chemistry

Thermodynamic arguments rarely explain anything in an absolute sense. They can, however, provide that essential first step towards understanding a chemical (or any other) problem - a rational restatement of the problem, and the factors which have to be considered in its solution. For example, consider the question Why is HF a weak acid in aqueous solution and the answer Because its pKa is 3.17 at 25°C, which means that AG° for its dissociation is 18kJmol l the dissociation is thermodynamically unfavourable . This answer does not immediately explain why HF is a weak acid but it does set out the 

Some thermodynamic data relevant to the stability of hydrogen peroxide are summarised below (all energies in kJ mol-1 at 25 °C)  

This elusive compound was the subject of much theoretical speculation prior to its preparation in 1976. Repeated failures to obtain it by the most obvious methods led to the general conclusion that the reaction  

In Chapter 6 we will have much to say about a closely-related substance, PH3F2, which is thermodynamically stable to reactions such as  

The latter reaction clearly demands a bimolecular rate-determining step, and will be slow at low temperatures and low pressures. Thus PH3F2 can be obtained as a reasonably stable gaseous substance at room temperature. 

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