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  4. 1 g of water is evaporated at 1 atmospheric pressure. Its volume in liquid phase is 1 cm 3 which becomes 1671 cm 3 in the vapour phase. If the latent heat of water is 2256 J / g , then change in its internal energy is

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Q. 1 g of water is evaporated at 1 atmospheric pressure. Its volume in liquid phase is $1 \,cm ^{3}$ which becomes $1671 \,cm ^{3}$ in the vapour phase. If the latent heat of water is $2256 \,J / g $, then change in its internal energy is

Thermodynamics

Solution:

$\Delta Q=\Delta U+P \Delta V$
For $1 g$ of water, $\Delta Q=2256 J$
$\Delta W=P \Delta V=\left(1.013 \times 10^{5} Pa \right)\left[1670 \times 10^{-6}\right] m ^{3}=169 J$
$\Rightarrow \Delta U=\Delta Q-P \Delta V=(2256-169) J =2087 J$