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 figure.
After sparking $A$ dissociates according to following reaction
$A\left(g\right)⟶B\left(g\right)+3C\left(g\right)$
If pressure of Gas $A$ decreases to $0.9atm$. Then
(Assume temperature to be constant and is $300K$)

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

Answer 1

The correct option is A total pressure increased to $1.3$ atm

Given

Initial pressure of A gas is 1 atm

After sparking A dissociates into B and C

Pressure of A decreases to 0.9 atm

Solution

Let x be the decrease in Pressure of A

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

t=0 1 0 0

t=t 1-x x 3x

We know that

1-x=0.9

x= 0.1 atm

Total pressure of system at equilibrium is

=1 - x + x + 3x

=1.3 atm

The correct option is A