Question

A compound exists in the gaseous phase both as a monomer (A) and dimer $\left(A_2\right)$. The molar mass of A is 48. In an experiment, 96 g of the compound was confined in a vessel of volume 33.6 litre and heated to ${273}^{o}C$. Calculate the pressure (in atm) developed, if the compound exists as a dimer to the extent of 50% by mass under these conditions.

Answer 1

Since, A and $A_2$ are two states in the gaseous phase having their mass ratio 50%, i.e., 1:1

Mole of A$=\frac{96}{2}\times \frac{1}{48}=1(n=\frac{w}{M})$

Mole of $A_2=\frac{96}{2}\times \frac{1}{96}=\frac{1}{2}$

Total mole of A and $A_2$ are $=1+\frac{1}{2}=\frac{3}{2}$

Now, $PV=nRT$

$P\times 33.6=\frac{3}{2}\times 0.0821\times 546$

$P=2atm$