Question

Given the following data: H3PO4(aq) H+ H2PO4-(aq) ∆Hof(kJ/mol) -1288.3 0 -1285 ∆S (J/mol.K ) 158.2 0 89 (ΔGo = ΔHo -T ΔS; lnK = ΔGo/-RT) Calculate: 1. Standard free energy 2. K phosphoric acid and 3. Comment on the thermodynamic factors ( calculated ∆Ho and ∆S) that account/s for the fact that H3PO4 is a weak acid.

Answer 1

First calculate deltaS and deltaHrexn.

Then deltaG.

Then using this calculate ka value.

We find that ka is very less thus acid is weak