1 g of water, of volume 1 cm³ at 100, is converted into steam at same temperature under normal atmospheric pressure ( 1 × 10⁵ Pa). The volume of steam formed equals 1671 cm³. If the specific latent heat of vaporisation of water is 2256 J/g, the change in internal energy is, (a) 2256 J (b) 2423 J (c) 2089 J (d) 167 J

1 g of water, of volume 1 cm³ at 100, is converted into steam at same… | NEET 2019

Q17NEET 2019Medium

Heat, Work & First Law of Thermodynamics

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

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Answer: (c)

Heat absorbed: $Q = mL = 1 \times 2256 = 2256\text{ J}$
Work done by expansion: $W = P\Delta V = 10^{5} \times (1671 - 1)\times10^{-6} = 167\text{ J}$
$\Delta U = Q - W = 2256 - 167 = 2089\text{ J}$
So the answer is (c) 2089 J.

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