Reply to comment on: ‘Thermodynamic cycles and the calculation of pKa’ [Chem. Phys. Lett. 367 (2003) 145]

In the comment on my Letter about the use of the thermodynamic cycles to calculate pKa, da Silva and co-workers claim that my approach is incorrect due to an erroneous expression used for the chemical potential of water. In this reply, I have presented a rigorous statistical mechanics derivation of the chemical potential of liquid water, which shows that the expression for the chemical potential that I have used is correct. This result supports the previous conclusion that the thermodynamic cycle used by da Silva et al. leads to thermodynamically inconsistent equation for calculating the pKa.