Liquid ammonia is used in ice factory for making ice from water. If water at 200C is to be converted into 2kg ice at 00C, how many grams of ammonia are to be evaporated? (Given: The latent heat of vaporization of ammonia = 341cal/g)
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Solution
Amount of heat energy released in cooling 2kg water from 200C to 00C = 2×1000×1×20=40000cal.
Amount of heat energy released in converting 2kg water at 00C to ice = 2×1000×80=160000cal.
Thus, total energy required in converting water at 200C to ice = 40000+16000=200000cal.
Grams of ammonia to be evaporated = 200000341=586.5g.