Question

$X{Y}_2$ dissociates as $X{Y}_{2\left(g\right)}\rightleftharpoons X{Y}_{\left(g\right)}+Y_{\left(g\right)}$. When the initial pressure is $600$ mm of Hg, the total pressure at equilibrium developed is $800$ mm of Hg.

Therefore, the pressure of $Y$ at equilibrium is:

• A. $200$
• B. $50$
• C. $100$
• D. $150$

Answer 1

Answer: (A)

$200$

Given that the initial pressure is $600$ mm of Hg and the total pressure is $800$ mm of Hg.

The equilibrium reaction is $X{Y}_{2\left(g\right)}\rightleftharpoons X{Y}_{\left(g\right)}+Y_{\left(g\right)}$.

Let $p$ represents the change in pressure.

	$X{Y}_2$	$XY$	$Y$
Initial	$600$	$0$	$0$
Change	$-p$	$p$	$p$
Equilibrium	$(600-p)$	$p$	$p$

Total pressure $=600-p+p+p=800$ or $p=800-600=200$ mm of Hg.

Thus, the equilibrium pressure of $Y$ is $200$ mm of Hg.

$A$ is the correct answer.