Q. At 373 K, a gaseous reaction $A \rightarrow 2B + C$ is found to be of first order. Starting with pure$\ A,$ the total pressure at the end of 10 min was 176 mm and after a long time when $A$ was completely dissociated, it was 270 mm. The pressure of $A$ at the end of 10 min was
A) 94 mm
B) 47 mm
C) 43 mm
D) 90 mm
Explanation
(b)
For the reaction : $A \rightarrow \ 2B\ + \ C$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ p_{1}\ \ \ \ \ \ \ 0\ \ \ \ \ \ \ \ \ 0$
After 10 min $\ \ \ \ \ \ p_{1} - p\ \ \ \ 2p\ \ \ \ \ \ \ p$
After long time $\ \ \ \ \ 0\ \ \ \ \ \ \ \ \ \ 2p_{1}\ \ \ \ \ p_{1}$
Total pressure $= \left( p_{1} - p + 2p + p \right) = 176\ mm$
Total pressure after long time
$= 2p_{1} + p_{1} = 270\ mm$
Calculate the value of $p$ from above two equation and then the difference of $p_{1}\ and\ p$ will be the pressure of $A$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.