pBlock ElementsII 2 Question 39
42. Give reasons in two or three sentences only for
(i) Bond dissociation energy of $\mathrm{F}{2}$ is less than that of $\mathrm{Cl}{2}$.
(ii) Sulphur dioxide is a more powerful reducing agent in the alkaline medium than in acidic medium.
(1992, 2M)
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Solution:
- (i) Due to small size and high electron density of fluorine atom, there exist a significant repulsions between fluorine atoms in $\mathrm{F}{2}$, they have greater tendency to get apart. Hence, bond energy of $\mathrm{F}{2}$ is less than that of $\mathrm{Cl}_{2}$. This is against to bond-length bond-energy relationship,. (ii) Sulphur dioxide is a more powerful reducing agent in alkaline medium because nascent hydrogen is produced in the presence of moisture
i.e. $\mathrm{SO}{2}+2 \mathrm{H}{2} \mathrm{O} \longrightarrow \mathrm{H}{2} \mathrm{SO}{4}+2 \mathrm{H}$
And alkaline solution neutralises the acid i.e. $\mathrm{H}{2} \mathrm{SO}{4}$ and shift the equilibrium in the forward direction producing more nascent hydrogen. But in acidic medium the equilibrium will suppressed resulting in a lesser amount of nascent hydrogen.
