Question

What is the general chemical equation of photosynthesis? Why doesn't that equation clearly show the real origin of the molecular oxygen liberated?

Answer 1

The general equation of photosynthesis is:

6 CO₂ + 6 H₂O + light --> C₆H₁₂O₆ + 6 O₂.

Water molecules are also produced in the chemical stage of photosynthesis as the following complete equation reveals:

6 CO₂ + 12 H₂O + light --> C₆H₁₂O₆ + 6 H₂O + 6 O₂

Water molecules are present in the reagent side as well in the product side of the equation. Pure mathematical simplification of stoichiometric coefficients, however, leads to elimination of water from the product side and it then seems that 6 molecules of molecular oxygen (O₂), i.e., 12 atoms of oxygen, are made for each 6 molecules of water, i.e., 6 oxygen atoms, in the reagent side. Thus a false impression that 6 other oxygens come from carbon the dioxide is created.