= Solution
\b[Association in solution includes replacement of solute–<solvent> contacts, not just formation of the isolated dimer.] <cyclohexane> solvates the <benzene> surface well through dispersion. Much of the London dispersion gained on bringing two <benzene> <molecules> together replaces comparable <benzene>–<cyclohexane> contacts, leaving only a modest net gain before the translational and orientational <entropy> penalty. <cyclohexane> cannot provide the complementary donor/acceptor interactions available when two <waters> <hydrogen>-bond, so <water> association gains a more distinctive interaction relative to its separated solvated monomers.
Using the same concentration <standard state>, $K^\circ=K_c c^\circ$ and $\Delta G^\circ_{\rm assoc}=-RT\ln K^\circ$. For illustration at 298 K and $c^\circ=1\ \mathrm{mol\,L^{-1}}$, the ratio of the two supplied <association constants> corresponds to
$$
\Delta G^\circ_{\rm water}-\Delta G^\circ_{\rm benzene}=-RT\ln(1/0.03)\simeq\boxed{-8.69\ \mathrm{kJ\,mol^{-1}}}.
$$
Thus the <water>-<molecule> pair can associate more favourably in this <solvent> even though the stipulated isolated-pair binding energies are similar. Gas-phase potential energy alone omits both differential <solvation> and the <entropy> of association.
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