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Q. The latent heat of ice is 80 Cal/g. The change in entropy when 10 gram of ice at $0 {^{\circ}C}$ is converted into water of same temperature is

UPSEEUPSEE 2019

Solution:

The change in entropy of a system is given as
$\Delta S = \frac{\Delta Q}{T} $
where, $T = $ temperature and $\Delta Q =$ heat absorbed by the system.
Here, latent heat of ice, $L = 80$ cal/g, mass of water, $m= 10 \,g$ and temperature,
$T = 0^{\circ}C = 273\,K$
Heat given to $10 \,g$ ice,
$E = mL = 10 \times 80$
$\Rightarrow E = 800 \,cal$
So, the entropy change
$\Delta s =\frac{E}{T} = \frac{800}{273}$
$\Rightarrow s = 2.93 \, cal/K$