Chemistry - Mole Concept Question with Solution | TestHub

${\mathrm{C}}_6{\mathrm{H}}_6(\mathrm{g})+3{\mathrm{H}}_2(\mathrm{g})\to {\mathrm{C}}_6{\mathrm{H}}_{12}(\mathrm{g})$

Let x and y be the partial pressures (initial) of gaseous benzene and hydrogen in the vessel.

Then, $\mathrm{x}+\mathrm{y}=60\dots \left(i\right)$

After the reaction, whole of benzene is converted to cyclohexane.

Partial pressure of cyclohexane $=\mathrm{x}\mathrm{mm}\mathrm{Hg}$

Partial pressure of hydrogen left unreacted $=y-3x$

Total pressure of the system after the reaction,

$$x+y-3x=y-2x=30\dots \left(ii\right)$$

Solving (i) and (ii), $\mathrm{x}=10\mathrm{mm}\mathrm{Hg}$

Number of moles $\propto$ pressure; Volume $\propto$ number of moles.

Hence, fraction of benzene by volume in the original mixture $=\frac{10}{60}=\frac{1}{6}=0.167$