Question

A manometer attached to a flask contains with ammonia gas have no difference in mercury level initially as shown in diagram. After sparking into the flask, ammonia is partially dissociated as $2N{H}_3\left(g\right)\to N_2\left(g\right)+3H_2\left(g\right)$ now it has a difference of 6 cm in mercury level in two columns, what is partial pressure of $H_2\left(g\right)$ at equilibrium?

• A. $9cmHg$
• B. $18cmHg$
• C. $27cmHg$
• D. None of these

Answer 1

The correct option is A $9cmHg$

At equilibrium,
$\begin{array}{cccc}& 2N{H}_3\left(g\right)\leftrightharpoons & N_2\left(g\right)& +3H_2\left(g\right)\\ \text{Before sparking}& 76& 0& 0\\ \text{After sparking}& 76-2x& x& 3x\end{array}$

According to the question, after sparking the difference in mercury levels in the two columns is 6.

So basically, $2x=6$
$\Rightarrow x=3$

Thus partial pressure of $H_2$ be $3x=3\times 3=9cmHg$