Question

Consider the reaction:

\[\ce{6 CO2(g) + 6H2O(l) → C6 H12O6(aq) + 6O2(g)}\]

Why it is more appropriate to write these reaction as:

\[\ce{6CO2(g) + 12H2O(l) → C6 H12O6(aq) + 6H2O(l) + 6O2(g)}\]

Also, suggest a technique to investigate the path of the redox reactions.

Answer 1

The process of photosynthesis involves two steps.

Step 1:

H₂O decomposes to give H₂ and O₂.

Step 2:

The H₂ produced in step 1 reduces CO₂, thereby producing glucose (C₆H₁₂O₆) and H₂O.

\[\ce{6CO_{2(g)} + 12H_{2(g)}  -> C_6H_12O_{6(s)} + 6H_2O_{(l)}}\]

Now, the net reaction of the process is given as:

\[\ce{2H_2O_{(l)} -> 2H_{2(g)} + O_{2(g)} ] × 6}\]

\[\ce{6CO_{2(g)} + 12H_{2(g)} -> C_6H_12O_{6(g)} + 6H_2O_{(l)}}\]

\[\ce{6CO_{2(g)} + 12H_2O_{(l)} -> C_6H_12O_{6(g)} +  6H_2O_{(l)} + 6O_{2(g)}}\]

It is more appropriate to write the reaction as given above because water molecules are also produced in the process of photosynthesis.

The path of this reaction can be investigated by using radioactive H₂O₁₈ in place of H₂O.