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

Oct 21, 2017

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

#### Explanation:

$6 C {O}_{2} \left(g\right) + 24 {H}^{+} + 24 {e}^{-} \rightarrow {C}_{6} {H}_{12} {O}_{6} \left(a q\right) + 6 {H}_{2} O \left(l\right)$

Here we go from $C \left(+ I V\right)$ to $C \left(0\right)$

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

${H}_{2} O \left(l\right) \rightarrow \frac{1}{2} {O}_{2} + 2 {H}^{+} + 2 {e}^{-}$

Here we go from $O \left(- I I\right)$ to $O \left(0\right)$

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

$\cancel{12} 6 {H}_{2} O \left(l\right) + 6 C {O}_{2} \left(g\right) + \cancel{24 {H}^{+}} + \cancel{24 {e}^{-}} \rightarrow {C}_{6} {H}_{12} {O}_{6} \left(a q\right) + \cancel{6 {H}_{2} O \left(l\right)} + 6 {O}_{2} + \cancel{24 {H}^{+}} + \cancel{24 {e}^{-}}$

To give finally.....

$6 C {O}_{2} \left(g\right) + 6 {H}_{2} O \left(l\right) \stackrel{h \nu}{\rightarrow} {C}_{6} {H}_{12} {O}_{6} \left(a q\right) + 6 {O}_{2} \left(g\right)$

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?