Q11 / 180 · COMEDK 2018 · Chemistry

4 moles each of $\mathrm{SO}_{2}$ and $\mathrm{O}_{2}$ gases are allowed to react to form $\mathrm{SO}_{3}$ in a closed vessel. At equilibrium $25 \%$ of $\mathrm{O}_{2}$ is used up. The total number of moles of all the gases present at equilibrium is

  • A
    $6.5$
  • Correct answer
    B
    $7.0$
  • C
    $8.0$
  • D
    $2.0$

Solution

$$ \begin{aligned} &\begin{array}{lccc} & 2 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightleftharpoons & 2 \mathrm{SO}_{3} \\ \text { Initially } & 4 \text { moles } & 4 \text { moles } & 0 \\ \text { At equili. } & (4-2) & (4-0.25 \times 4) & 2 \\ & =2 & =3 & \end{array}\\ &\therefore \text { Total moles at equilibrium }=2+3+2=7 \text { moles. } \end{aligned} $$

Hence, the correct answer is option: 'B'.

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