Question

A heat engine operates between 200 K and 100 K. In each cycle it takes 100 J from the hot reservoir, loses 25 J to the cold reservoir, and does 75 J of work. This heat engine violates the second law but not the first law of thermodynamics. Why is this true?

Answer 1

The heat engine violates the second law of thermodynamics but not the first law because it transfers heat from a lower temperature reservoir to a higher temperature reservoir. Heat always flows spontaneously from a higher temperature region to a lower temperature region.

Step-by-step explanation:

A heat engine operates between two reservoirs, a hot reservoir and a cold reservoir, and converts thermal energy into mechanical work. It follows the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred or transformed. The first law is not violated in this case because the engine takes 100 J of heat from the hot reservoir and does 75 J of work, so the remaining 25 J is transferred to the cold reservoir. However, the engine violates the second law of thermodynamics because it transfers heat from a lower temperature reservoir to a higher temperature reservoir, which is not possible according to the second law. In a heat engine, heat always flows spontaneously from a higher temperature region to a lower temperature region.

Answer 2

It does not violate the first law because the total energy taken is what is used 100J = 25J + 75J

But violates 2nd lawbecause the engine has a higher energy after doing work than the initial for e.g A cold object in contact with a hot one never gets colder, transferring heat to the hot object and making it hotter confirming the second law