Question

At $730^{\circ }C$ the vapour density of iodine under a pressure of $1$ atm is $97.45\%$ of the theoretical value, on the assumption that the molecule of gaseous iodine is diatomic. What is the degree of dissociation of $I_2$ ?

• A. 0.0131
• B. 0.0262
• C. 0.082
• D. 0.0324

Answer 1

Answer: (B)

van't Hoff factor $(i)=\frac{\text{ Theoretical value of mol. wt. }}{\text{ Observed value of mol. wt. }}$



Total number of moles at equilibrium $=1-\alpha +2\alpha =1+\alpha$

Observed molecular wt. $=\frac{97.45}{100}\times 254=247.52$

$\therefore i=1+\alpha$

$\Rightarrow \frac{254}{247.52}=1+\alpha$

$247.52\alpha =254-247.52=6.48$

$\Rightarrow \alpha =\frac{6.48}{247.52}=0.0262$