Question

A open ended mercury manometer is used to measure the pressure exerted by a trapped gas as shown in the figure. Initially manometer shows no difference in mercury level in both columns as shown in diagram.
After sparking ${}^{\prime }{A}^{\prime }$ dissociates according to following reaction
$A\left(g\right)\to B\left(g\right)+3C\left(g\right)$
If pressure of Gas $"A"$ decrease to $0.9$ atm. Then:
(Assume temperature to be constant and is $300K$).

• A. total pressure increased to $1.3atm$
• B. total pressure increased by $0.3atm$
• C. total pressure increased by $22.3cm$ for $Hg$
• D. difference in mercury level is $228mm$

Answer 1

Answer: (A), (D)

The correct options are
A total pressure increased to $1.3atm$
D difference in mercury level is $228mm$

After sparking ${}^{\prime }{A}^{\prime }$ dissociates :

$A\left(g\right)\to B\left(g\right)+3C\left(g\right)$

Now, the initial pressure of $A=76cm$ of $Hg$ $=1atm$

the pressure of gas $A$ decreases to $0.09$ atm.

Gas $A$ having pressure $0.1$ atm reacts to produce $B$ having pressure $0.01$ atm and $C$ having pressure $0.3$ atm.

$\therefore$ Total pressure at equilibrium $=0.9+0.1+0.3=1.3atm$

Thus total pressure increase by $0.3$ atm.

i.e. equivalent to $=0.3\times 760mm$ of $Hg$

$=228mm$ of $Hg$

$\therefore$ difference in mercury level is $228mm$

Ans (A) and (D).