How is photosynthesis an example of an oxidation-reduction reaction?

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Answer 1 · 2017-10-21T17:31:49

Well, carbon dioxide is REDUCED to glucose......

$6CO_2(g) +24H^+ +24e^(-) rarr C_6H_12O_6(aq) +6H_2O(l)$

Here we go from $C(+IV)$ to $C(0)$

And water is OXIDIZED to dioxygen gas.....

$H_2O(l) rarr 1/2O_2 + 2H^(+) + 2e^(-)$

Here we go from $O(-II)$ to $O(0)$

And so we add ONE of the former reaction, to TWELVE of the latter reactions....in order to remove the electrons.....

$cancel(12)6H_2O(l) +6CO_2(g) +cancel(24H^+) +cancel(24e^(-))rarr C_6H_12O_6(aq) +cancel(6H_2O(l))+6O_2 + cancel(24H^(+)) + cancel(24e^(-))$

To give finally.....

$6CO_2(g) +6H_2O(l)stackrel(hnu)rarr C_6H_12O_6(aq) +6O_2(g)$

And this reaction is ENDOTHERMIC (and this is reasonable, because we break STRONG $C=O$ and $H-O$ bonds). What do you think supplies the energy?