The free energy for the oxidation of glucose to co2 and water is -685 kcal/mol and the free energy for the reduction of nad+ to nadh is +52 kcal/mol. why are only two molecules of nadh generated during glycolysis when the energy differences could allow as many as a dozen to be formed?

The complete oxidation of glucose molecule includes glycolysis, oxidative decarboxylation and krebs cycle

Explanation:

Energetic balance of glucose molecule oxidation:

*- glycolysis: 2 ATP + 2 NADH + H+

*- oxidative decarboxylation: 1 NADH + H+ per reaction (2 NADH + H+ total)

*- krebs cycle: 3 NADH + H+ + 1 FADH2 + 1 GTP per cycle (6 NADH + H+ + 2 FADH2 + 2 GTP total)

After complete the electron chain transport and oxidative phosphorylation the final balance is 36 (38) ATP