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 $"A"$ decreases to $0.9atm$. 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 $22.3cm$ of $Hg$
• D. difference in mercury level is $228mm$.

Answer 1

Answer: (A), (B), (D)

The correct options are
A total pressure increased to $1.3atm$
B total pressure increased by $0.3atm$
D difference in mercury level is $228mm$.

The change in the number of moles $\Delta n=4-1=3$
Initial pressure is equal to 76 $cm$ of mercury or 1 $atm$.
$1-0.9=0.1$ $atm$ of $A$ will react to form products which will exert a pressure of 0.4 $atm$.
Total pressure increased to $1.3atm$
Total pressure increased by $0.3atm$
The difference in mercury level is $228mm$.
$P_T=(1+3\times 0.1)=1.3atm$
$△P=0.3atm$ or $76\times 0.3cmofHg$
or $760\times 0.3=228mmofHg$