Question

1g of water, of volume 1 cm$^3$ at 100?C, is converted into steam at same temperature under normal atmospheric pressure ($\simeq$ ) $1\times 10^5$Pa . The volume of steam formed equals 1671 cm$^3$. If the specific latent heat of vaporisation of water is 2256 J/g, the change in internal energy is,

• A. 2423 J
• B. 2089 J
• C. 167 J
• D. 2256 J

Answer 1

Answer: (B)

2089 J

Answer 2

$Q = \Delta U + W$
$\Rightarrow mL = \Delta U + P(V_2 - V_1)$
$\Rightarrow 1(2256) = \Delta U + 1 \times 10^5 (1670 \times 10^{-6})$
$\Rightarrow \Delta U = 2089 \,J$