Discussion Forum



1)

The temperature of an open room of volume 30 m3  increases from 17° C to 27° C due to the sunshine . The atmosphere pressure in the room remains 1× 105 Pa. If ni and nf  are the number of molecules in the room before and after heating , then nf  -ni will be


A) $1.38\times 10^{23}$

B) $2.5\times 10^{25}$

C) $-2.5\times 10^{25}$

D) $-1.61\times 10^{23}$

Answer:

Option C

Explanation:

From $pV=nRT=\frac{N}{N_{A}}RT$

    We have, $n_{f}-n_{i}=\frac{pVN_{A}}{RT_{f}}-\frac{pVN_{A}}{RT_{i}}$

$\Rightarrow n_{f}-n_{i}=\frac{10^{5}\times30}{8.30}\times6.02\times 10^{23}$

    $(\frac{1}{300}-\frac{1}{290})$

   $=-2.5\times 10^{25}$

$\therefore$     $\triangle n =-2.5\times 10^{25}$