Question

A manometer attached to a flask contains ${NH}_3$ gas have no difference in mercury level initially as shown in the diagram. After the sparking into the flask, it has a difference of $19cm$ in mercury level in two columns. Calculate % dissociation of ammonia.

Answer 1

Initially no height difference So $P_0=760$ mm of $Hg$

${NH}_3\rightleftharpoons \frac{1}{2}{N}_2+\frac{3}{2}{H}_2$ or

$P_0$ $0$ $0$

$P_0(1-\alpha )$ $P_0\alpha /2$ $3P_0\alpha /2$

$\underset{}{P_0}(1+\alpha )$ new pressure at equilibrium

$76cm(1+\alpha )=(19cm+76cm)$

$1+\alpha =(1+19/76)$ % of dissociation

$\alpha =1/4$ $\alpha \times 100=25$%