Question

A flask of one litre capacity containing $N{H}_3$ at 1 atm and ${25}^{o}C$. A spark is passed through until all the $N{H}_3$ is decomposed into $N_2$ and $H_2$. Calculate the pressure (in atm) of gases left at ${25}^{o}C$.

Answer 1

The given reaction is $2N{H}_2\to N_2+3H_2$

For $N{H}_3:P=1atm,V=1litre,T=298K$

mole of $N{H}_3=\frac{PV}{RT}=\frac{1\times 1}{0.0821\times 298}$

$=4.087\times {10}^{-2}$

Since, 2 mole of $N{H}_3$ are used and 4 mole of $N_2$ and $H_2$ are formed.

Therefore, at the same T and V, $P\propto n$

$\frac{P_1}{P_2}=\frac{n_1}{n_2}$ or $\frac{1}{P}=\frac{2}{4}$

Pressure after reaction $=2atm$