Answer
Due to three hydrogen bonds, the free energy difference between Y and X is -3 kcal/mole. (The free energy of Y is lower than that of X, because energy would need to be expended to break the bonds to convert Y to X. Therefore the value for deltaG for the transition X --> Y is negative.) The equilibrium constant for the reaction is about 100 (from table 3-1, p.96); i.e., there are 100 times more molecules of Y than of X at equilibrium. An additional three hydrogen bonds would increase deltaG to -6 kcal/mole and increase the equilibrium constant another 100 fold to 10^4. Thus, relatively small differences in energy can have a major effect on equilibria.
Work Step by Step
Due to three hydrogen bonds, the free energy difference between Y and X is -3 kcal/mole. (The free energy of Y is lower than that of X, because energy would need to be expended to break the bonds to convert Y to X. Therefore the value for deltaG for the transition X --> Y is negative.) The equilibrium constant for the reaction is about 100 (from table 3-1, p.96); i.e., there are 100 times more molecules of Y than of X at equilibrium. An additional three hydrogen bonds would increase deltaG to -6 kcal/mole and increase the equilibrium constant another 100 fold to 10^4. Thus, relatively small differences in energy can have a major effect on equilibria.
