Physics
(a) Why does it become pleasantly warm when the lakes start freezing?
(b) Water freezes to form ice. What change would you expect in the average kinetic energy of the molecules?
(c) Which will contain more heat energy 1 g of ice at 0°C or 1 g water at 0°C ?
Calorimetry
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Answer
(a) The surroundings become pleasantly warm when water in a lake starts freezing because the specific latent heat of fusion of ice is very high, hence large quantity of heat is released when the water in the lake freezes. Therefore, the temperature of the surrounding becomes pleasantly warm.
(b) The average kinetic energy of the molecules decreases as water freezes to produce ice because the temperature of the water molecules drops, and they hold to one another to form a crystal.
(c) 1 g of water at 0° C has more heat energy because 1 g of water at 0° C liberates 80 cal heat to form 1 g of ice at 0° C.
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