Question

An open manometer attached to a flask containing ammonia gas have no difference in mercury level initially as shown in diagram. After sparking into the flask, ammonia is partially dissociated as $2 \mathrm{NH}_3(\mathrm{~g}) \longrightarrow \mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g})$ . Now it have difference of $\text{18} \, \text{cm}$ in mercury level in two columns, what is partial pressure of $\mathrm{H}_2(\mathrm{~g})$ at equilibrium ?

• A. $\text{9} \, \text{cm}$ of $\text{Hg}$
• B. $\text{18 cm}$ of $\text{Hg}$
• C. $\text{27} \, \text{cm}$ of $\text{Hg}$
• D. None of these

Answer 1

Answer: (C)

$\underset{76-2x}{2NH_{3}(g)} \to \underset{x}{N_{2}(g)}+\underset{3x}{3H_{2}}$
$7 6 + 2 \text{x} = 7 6 + 1 8$

$2 \text{x} = 1 8$

$∴ \, \, \text{x} = 9$

$∴ \, \text{p}_{\text{H}_{2}} = 3 \times 9$

$= \text{ 27 cm of Hg}$