Question

At 373 K,a gaseous reaction $A\to 2B+C$ is found to be of first order.Starting with pure A,the total pressure at the end of 10 min was 176 mm of Hg and after a long time when A was completely dissociated,it was 270 mm of Hg.The pressure of A at the end of 10 minutes was:

• A. 94 mm of Hg
• B. 47 mm of Hg
• C. 43 mm of Hg
• D. 90 mm of Hg

Answer 1

Answer: (B)

The correct option is B 47 mm of Hg
$A\to 2B+C$

$att=0$ $x$ $0$ $0$

$att=10$ $x-y$ $2y$ $y$

$total=x-y+2y+y$

$=x+2y=176mm$-------$\left(i\right)$

$att=100$ $0$ $2x$ $x$

$total=2x+x=270mm$

$\Rightarrow 3x=270$

$\Rightarrow x=90mmofHg$

put the value of $A$ in $e{q}^n\left(i\right),$ we get

$x+2y=176$

$\Rightarrow 90+2y=176$

$\Rightarrow 2y=86$

$\Rightarrow y=43mmofHg$

At the end of $10$ min pessure of $A$ is $x-y=90-43=47mmofHg$

Option B is correct.