Question

Question 8.9 Consider the reactions:

(a) 6 CO2(g) + 6H2O(l)→C6 H12 O6(aq) + 6O2(g)

(b) O3(g) + H2O2(l)→H2O(l) + 2O2(g)

Why it is more appropriate to write these reactions as:

(a) 6CO2(g) + 12H2O(l)→C6 H12 O6(aq) + 6H2O(l) + 6O2(g)

(b) O3(g) + H2O2 (l)→H2O(l) + O2(g) + O2(g)

Also suggest a technique to investigate the path of the above (a) and (b) redox

reactions.

Class XI Redox Reactions Page 272

Answer 1

Hi

Here is your answer,

Mechanism of photosynthesis 

STEP 1:- 12H₂O(l) → 12H₂(g) + 6O₂(l)  { DECOMPOSITION REACTION } 

STEP 2  :-  6CO₂(g)  + 12H₂O(g)  → C₆H₂O₆(s) + 6H₂O(l)

  (H₂ formed in this step reduce CO₂ to C₆H₁₂O₆  in second step)

 Hence, it is more appropriate to write the equation for photosynthesis as follows. ( BY ADDING 1 AND STEP 2 )

                   6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂

Actually in the process of photosynthesis 12H₂O are used up in the first step and 6H₂O are formed per molecule of glucose ( carbohydrates )

b) Mechanism of reaction of ozone with H₂O₂

STEP 1 :-     O₃(g) →  O₂(g) + O(g)

STEP 2 :-  H₂O₂ + O(g) → H₂O₂ + O₂(g)

 ↔In first step ozone liberates nascent oxygen , it oxides H₂O₂  in step 2. Therefore, overall reaction is as follows

                          H₂O₂ + O   → H₂O₂ + O₂ + O₂
  
 ↔ In overall reaction, O₂  is written by two times because it is released in each of the two steps.



Hope it helps you !

Answer 2

(a) Mechanism of photosynthesis is very complex but broadly it may be visualized to occur in two steps .

step 1 :- decomposition of water to give H2 and O2 in the presence of chlorophyll .
12H2O(l) ---------> 12H2(g) + 6O2(g)

step 2 :- H2 produced C6H12O6 by reducing CO2 during this some H2O molecule are also produced as shown below.
6CO2(g) + 12H2(g) ------>C6H12O6(s) + 6H2O(l)

now, add equations , we get ,
6CO2(g) + 12H2O(l) ------->C6H12O6(s) + 6H2O(l) + 6O2(g) this is more appropriate to write the equation for photosynthesis because it emphasize that 12H2O are used per molecule of carbohydrate formed 6H2O are produced during this process.


(b) Mechanism of reaction of ozone with peroxide .
step 1:- O3(g) -----> O2(g) + [O] {nascent oxygen}
step 2 :- H2O2 + [O] ----> H2O(l) + O2(g)
________________________________
H2O2 + O3 ----> H2O + O2 + O2
in overall reaction , O2 is written by two times because it is released in each steps of reaction.