Consider the reactions :
(a) `6 CO_(2) (g) + 6 H_(2)O (1) to C_(6) H_(12) O_(6) (aq) + 6 O_(2)(g)`
(b) `O_(3)(g) + H_(2)O_(2)(1) + 2 O_(2)(g)`
Why it is more appropriate to write these reactions as :
(a) `6 CO_(2) (g) + 12 H_(2)O(1) to C_(6)H_(12)O_(6) (aq) + 6 H_(2)(1) + 6 O_(2)(g)`
(b) `O_(3)(g) + H_(2)O_(2)(1) to H_(2)(1) + O_(2)(g) + O_(2)(g)`
Also suggest a technique to investigate the path of the above (a) and (b) redox reactions .

Explanation

This reaction expresses the process of photosynthesis which is a very complicated process and occurs in several steps. In this reaction, 12H_(2)O` molecules first decompose to give `H_(2)` and `O_(2)` in the presence of chlorophyll and the `H_(2)` thus produced reduces `CO_(2)` to `C_(6)H_(12)O_(6)`. Thus, in a simple way, the reaction can be expressed as follows.
`{:(" "12H_(2)O(l)to12H_(2)(g)+6O_(2)(g)" "....(i)),(6CO_(2)(g)+12H_(2)(g)toC_(6)(g)+12H_(2)(g)toC_(6)H_(12)O_(6)(s)+6H_(2)O(l)......(ii)),(bar(6CO_(2)(g)+12H_(2)O(l)toC_(6)H_(12)O_(6)(s)+6H_(2)O(l)+6O_(2)(g))........(iii)):}
Therefore, it is more appropriate to write the reaction as (iii). This representation involves the participation of `12H_(2)O` molecules and liberation of `6H_(2)O` molecules in the reaction. (b) The given reaction actually takes place as follows:
`{:(" "O_(3)(g)toO_(2)(g)+O(g)" "......(i)),(H_(2)O_(2)(l)+O(g)toH_(2)O(l)+O_(2)(g)" "......(ii)),(bar(O_(3)(g)+H_(2)O_(2)(l)toH_(2)O(l)+O_(2)(g)+O_(2)(g))" "......(iii)):}`
The representation of the reaction as (iii) suggests that one `O_(2)` molecule is obtained from `O_(3)` while the other from `H_(2)O_(2)`. Therefore, it is a more appropriate representation of the reaction.
The path of the reactions (a) and (b) can he investigated by tracer technique, i.e., by using `H_(2)O^(18)` in reaction (a) and by using `H_(2)O_(2)^(18)` (or `O_(3)^(18)` ) in reaction (b).