Question

An open flask contains air at ${27}^{\circ }C$. At what temperature should it be heated so that $1/3rd$ of air present in it goes out?

• A. ${177}^{\circ }C$
• B. ${100}^{\circ }C$
• C. ${300}^{\circ }C$
• D. ${150}^{\circ }C$

Answer 1

Answer: (A)

${177}^{\circ }C$

Let initial number of moles of air at ${27}^{\circ }C\left(300K\right)=n$
At temperature $TK$, the no. of moles left $=n-\frac{n}{3}=\frac{2n}{3}$
At constant pressure and volume, $n_1{T}_2=n_2{T}_2$
$n\times 300=\frac{2n}{3}\times T\Rightarrow T=450K$ or ${177}^{\circ }C$.