Question

A compound exists in the gaseous phase both as a monomer ($A$) and as a dimer ($A_2$). The molecular mass of $A$ is $48gmo{l}^{-1}$. In an experiment, $96g$ of compound was confined in a vessel of volume $33.6L$ and heated to ${273}^{\circ }\text{C}$. Calculate the pressure (in atm, rounded off to the nearest integer) developed if the compound exists as a dimer to the extent of 50% by weight under these conditions.

Answer 1

Since, the compound contains equal weight of $A$ and $A_2$,
$\therefore \text{Moles of}A=\frac{96}{2}\times \frac{1}{48}=1$
and, $\text{Moles of}{A}_2=\frac{96}{2}\times \frac{1}{96}=\frac{1}{2}$
$\therefore \text{Total moles of}A\text{and}{A}_2\text{in the compound}=1+\frac{1}{2}=\frac{3}{2}$
From ideal gas equation,
$PV=nRT$
$P\times 33.6=\frac{3}{2}\times 0.0821\times 546$
$P=2\text{atm}$