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# Consider the Reactions 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: - CBSE (Science) Class 11 - Chemistry

ConceptOxidation Number Balancing of Redox Reactions

#### Question

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

#### Solution 1

(a)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.

6CO_(2(g)) + 12H_(2(g))  -> C_6H_12O_(6(s)) + 6H_2O_(l)

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

2H_2O_(l) -> 2H_(2(g)) + O_(2(g)) ] xx 6

6CO_(2(g)) + 12H_(2(g)) -> C_6H_12O_(6(g)) + 6H_2O_(l)

------------------------------------------------------------------------

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.

b) O2 is produced from each of the two reactants O3 and H2O2. For this reason, O2 is written twice.

The given reaction involves two steps. First, O3 decomposes to form O2 and O. In the second step, H2O2 reacts with the O produced in the first step, thereby producing H2O and O2.

O_(3(g)) -> O_(2(g)) + O_(g)

H_2O_(2(l)) + O_(g) -> H_2O_(l) + O_(2(g))

------------------------------------------------

H_2O_(2(l)) + O_(3(g))  -> H_2O_(l) + O_(2(g)) + O_(2(g))

The path of this reaction can be investigated by using H_2O_2^(18) or O_3^18.

#### Solution 2

12H_2O(l) -> 12H_2(g) + 6O_2(g)             ....(i)

6CO_2(g) + 12H_2(g) ->  C_6H_12O_6 (s)  + 6H_2O(l)   .....(ii)

----------------------------------------------------------

6CO_2(g) + 12 H_2O(l) -> C_6H_12O_6 (s) + 6H_2O(l) + 6O_2(g)   ......(iii)

(a) Therefore, it is more appropriate to write the equation for photosynthesis as (iii) because it emphasises that 12H2O are used per molecule of carbohydrate formed and 6H2O are produced during the process.

(b) The purpose of writing O2 two times suggests that O is being obtained from each of the two reactants.

O_3(g) -> O_2(g) + O(g)

H_2O_2 + O(g) -> H_2O(l) + O_2(g)

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O_3 (g) + H_2O_2 (l) -> H_2O(l) + O_2(g) + O_2(g)

The path of reactions (a) and (b) can be determined by using  H20218 or D20 in reaction (a) or by using  H20218 or O318in reaction (b).

Is there an error in this question or solution?

#### APPEARS IN

Solution Consider the Reactions 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: Concept: Oxidation Number - Balancing of Redox Reactions.
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