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A vessel holding 100 g of water at 0 deg C hangs in the middle of a room. In 15 minutes the water temperature rises by 2 deg C (steady heat gain from the surroundings). When an equal mass (100 g) of ice at 0 deg C is placed in the same vessel, it takes 10 hours to melt completely. From these data, find the latent heat of fusion of ice. (Take specific heat of water = 1 cal/g/deg C.)

1. 80 cal/g
2. 40 cal/g
3. 100 cal/g
4. 160 cal/g

Correct answer: 80 cal/g

Solution

Heat-gain rate = (100*1*2)/15 cal/min; over 600 min this supplies 8000 cal to melt 100 g of ice, giving L_f = 80 cal/g.

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