Question

$1\, g$ of water at $100^{\circ} C$ is completely converted into steam at $100^{\circ}\, C$. $1\, g$ of steam occupies a volume of $1650\, cc$. (Neglect the volume of $1\, g$ of water at $100^{\circ} C$ ). At the pressure of $10^{5} N / m ^{2}$, latent heat of steam is $540 \,cals / g$ $(1$ calorie $=4.2$ joule). The increase in the internal energy (in joule) is

• A. 2310
• B. 2203
• C. 1650
• D. 2150

Answer 1

Answer: (B)

Heat required to convert $1 g$ of water at $100^{\circ} C$
completely into steam at $100^{\circ} C$
$d Q=m L $
$=1 \times 540 $ calorie
$=540 \times 4.2=2268 \,J $
Work done in expanding volume
$d W =p d V=10^{5}\left(V_{2}-V_{1}\right) $
$=10^{5}(1650-1000) \times 10^{6}$
$=650 \times 10^{-1}=65 $
Increase in internal energy
$d U=d Q-d W=2268-65=2203\,J$