Question

$4$ moles each of $S{O}_2$ and $O_2$ gases are allowed to react to form $S{O}_3$ in a closed vessel. At equilibrium $25\%$ of $O_2$ is used up. The total number of moles of all the gases present at equilibrium is

• A. 6.5
• B. 7.0
• C. 8.0
• D. 2.0

Answer 1

Answer: (B)

$Att=0S{O}_2+$
$S{O}_2\text{ is the limiting reagent }$
$\text{ Att }=04-x4-\frac{x}{2}x$
$\Rightarrow 4-\left(\frac{x}{2}\right)\text{ is the oxygen remaining }$
$\Rightarrow \left(\frac{x}{2}\right)\text{ of oxygen is used up }$
$\Rightarrow \frac{x}{2}=0.25\times 4\Rightarrow x=2\text{ moles }$
$n_T=n_{50_3}+n_{0_2}+n_{50_2}$
$=(4-x)+4-\left(\frac{x}{2}\right)+x$
$\Rightarrow 8-\left(\frac{x}{2}\right)\Rightarrow 7\text{ moles }$