Question

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

• A. $94mm$
• B. $47mm$
• C. $43mm$
• D. $90mm$

Answer 1

The correct option is C $43mm$

A single gaseous molecule produces 3 molecules. The pressure of the system is 270 mm.

$p_a=\frac{270}{3}=90mmofHg$

If x is the decrease in the partial pressure of A at t = 10 min, then partial pressure of B and C is 2x and x

Total Pressure at this stage would be

$p_b+p_c+p_a=176mmofHg$

90 -x + 2x + x = 176 mm of hg

$x=43mmofHg$

So Option C is correct