An office worker claims that a cup of cold coffee on his table warmed up to 80°C by picking up energy from the surrounding air, which is at 25°C. Is there any truth to his claim? Does this process violate any thermodynamic laws?

ch1-2. problem: An office worker claims that a cup of cold coffee on his table warmed up to 80°C by picking up energy from the surrounding air, which is at 25°C. Is there any truth to his claim? Does this process violate any thermodynamic laws?

 

Answer: A cup of hot coffee is kept in the living room; after a certain period of time, the coffee gets cold. To heat the coffee we have to spend some energy. In our wash room, we get water by opening the tap (Valve). This water comes from the overhead tank which is located at an elevated place. To transfer this water back to the elevated place we need to spend some energy.So, from the above naturally occurring processes, we can say that heat flows from a higher temperature to lower temperature. Water flows from an elevated place to a lower place. Therefore, all the spontaneous processes occurring in nature are in one direction. To reverse the direction of process we need to spend energy. So, without any external work, it is impossible to raise the temperature of a body higher than the surrounding temperature. Therefore, there is no truth in his claim. It violates the second law of thermodynamics.

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