You are given three identical 2-liter Dewar flasks (vacuum flasks), A, B, and C,

Question

You are given three identical 2-liter Dewar flasks (vacuum flasks), A, B, and C, and an empty, smaller 600 mL flask D, which has thermally conducting walls. Flask D easily can be placed inside a Dewar flask. 1000 g of hot water at 80.0°C is poured into flask A, and 1000 g of cold water at 20.0°C is poured into flask B. Now, using all four containers, and without mixing the hot water with the cold water, is it possible to heat the cold water with the aid of the hot water so that the final temperature of the cold water will be higher than the final mperature of the hot water? No heat exchange with the surrounding air is permitted. v-1 merifir hrat canaityof water çan be taken as constant at 4.184 Jg K

Explanation / Answer

No , in any case it is not possible to heat the cold water with aid of the hot water so the the final temperature of the cold water will be higher than the final temperature of hot water. Because ,heat can only be transfer when the driving force would be present between two systems, here driving force is temperature gradient. As we put Hot water and cold water in indirect contact, the temperature of cold water increases and simultaneously the temperature of hot water decreases, as the heat is transferring from the hot water to cold water. So after some time a state come where the temperature of both water becomes almost equal. So the rate of heat transfer got decreases and when the temperature become equal the heat transfer stops, because at that stage there is no temperature gradient. So after that it is not possible to transfer heat form one water to another. So In the conclusion, the temperature of both water may become same but it is not possible to have final temperature of cold water greater than the hot water.

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