HOMOLYTIC BOND (H-A) DISSOCIATION FREE-ENERGIES IN SOLUTION - APPLICATIONS OF THE STANDARD POTENTIAL OF THE (H+/H.) COUPLE

Free energies of solvation [DELTA-G-solv(gas)aq'(s)] of the noble gases in water are linearly related to the atomic radii. These data allow DELTA-G(solv)(H.)aq to be calculated from the correlation line. The standard potential [E-degrees(H+/H.)aq] for reduction of the proton in water (reaction i) was then determined using eq ii. The value of E-degrees NHE(aq)(H+/H.)aq was observed to be -2.42 H+ + e- reversible H. (i) E-degrees NHE(aq)(H+/H.)aq = -(DELTA-G(solv)(H.)aq + DELTA-G(f)(H.)gas)/F (ii) V. Similarly, it was shown that the standard electrode potentials for the (H+/H.) couple in other solvents (S) can be determined using eq iii. The standard potentials for the (H+/H.)s couple are directly applicable in thermochemical cycles to the determination E-degrees NHE(S)(H+/H.)S = -(DELTA-G(solv)(H.)S + DELTA-G(f)(H.)gas)F (iii) of the differences in free energies of heterolysis and homolysis of bonds in solution. The bond dissociation energies obtained in this manner are subject only to the experimental errors in the determination of anion redox potentials E(A./A-)S and pK(a)'s of the corresponding conjugate acids (H-A's). A less rigorous treatment in which electrode potentials in S are referred to NHE(aq) using extrathermodynamic quantities is also discussed.