# How are the pKa's of very strong acids derived mathematically?

It is often said that "for very strong acids (HCl, H2SO4, etc.), the pKa value cannot be experimentally derived from standard titration and instead needs to be theoretically computed". However, I could not find any way to compute it theoretically. More specifically - I know that the pKa is a constant multiple of the logarithm of the (magnitude of the) Gibbs energy for deprotonation, and I know that the enthalpy part of the Gibbs energy can be computed easily (just decompose both sides into its constituent elements and use Hess' law), but I can't find any mathematical way to compute the entropy part on Wikipedia.

• – Mithoron Jan 16 at 1:27