Answering my own earlier question about oxygen and sugar:
It turns out that there is it possible, under standard temperature and pressure (STP), to measure the chemical potential of a molecule in units of kilogibbs (kilojoules per mole). There's even a small online database with the chemical potentials of several hundred common chemicals. A positive chemical potential means the molecule is unstable (at STP).
From the database and relevant to my question:
C6H12O6 (glucose in blood): -915.59
O2 (in tissue): -9.02
H2O (gaseous; strangely listed under OH2): -228.59
CO2 (in vein): -401.40
Given the reaction C6H12O6 + 6O2 => 6H20 + 6CO2 + heat
We can compute the energy released as heat: μ(C6H12O6) + 6 μ(O2) - 6 μ(H2O) - 6 μ(CO2)
which yields 2810.23 kilogibbs (kilojoules per mole)
Digging around online, I found that 1 mole of sugar is 180 grams, and a nutritional site told me this yields 2912 kJ. Close enough to 2810 for my back-of-the-envelope arithmetic. Yay for checking your work!
I don't see a way to answer my original question as phrased, but the oxygen has much more potential energy than the sugar.