Question

At ${100}^{0}C$ , the gaseous reaction $A\to 2B+C$ is found to be of first order. Starting with pure A, if at the end of 10 min, the total pressure of the system is 176 mm and after a long time it is 270 mm, the partial pressure of A at the end of 10 min is:

• A. 94 mm
• B. 43 mm
• C. 47 mm
• D. 176 mm

Answer 1

The correct option is C 47 mm

After a long time, the dissociation of A is complete. The dissociation of one mole of A gives 3 moles of products.

Hence, the initial pressure of $A=\frac{270}{3}=90mm.$

Let after 10 minutes the change in the pressure of A is x mm. The pressure of B and C would be 2x and x mm respectively.

Total pressure $=(90-x)+2x+x=(90+2x)mm.$

$90+2x=176mm$

$2x=(176-90)mm$

$x=43mm$

Thus the pressure of A after 10 minutes $=(90-x)mm=(90-43)=47mm$.

Hence, the correct option is $\text{C}$