Stability of Aqua Ions

Since Ln +(aq) is the most stable aqua ion, then both of the following processes are favoured. 

When is it most likely that Ln +(aq) ions will be stable For the first of the two reactions above to be favoured, the single factor that will help make A// positive is a high value of h. Less important would be the size of the ions, as this could affect the hydration enthalpies the difference between the hydration enthalpies will be less, the larger the lanthanide ions. Substituting into the above equation, we can investigate the relative stabilities of La +(aq) and Eu +(aq), making use of ionization energies from 

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