Anhydride and Condensation Reactions

Phosphoric acid is formed by the reaction of phosphorus pentoxide ( P2O5 = P4O10) with water  

The equilibrium of this reaction is virtually to the right-hand side. In a sequence of condensation equilibria, the monomer orthophosphoric acid (H3PO4) forms polyphosphoric acids, for example, (pyro-) diphosphoric acid (H4P2O7), triphosphoric acids (H5P3O10), and so on  

Metaphosphoric acid, (HP03) , is the formal limiting composition if only unbranched chains are formed. In addition to H[-0-P0(0H)-] 0H chains there are also [-0-P0(0H)-] rings, for example 

The equilibrium constants tQ of each equihbrium are functions of temperature and pressure  

if the thermodynamic equilibrium is estabhshed, the concentration of each polyphosphoric acid species is essentially a function of only temperature T and the initial concentration of P2O5. 

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