Question

29. Some of the energy that comes from burning fossil fuel can be turned into electricity, butsome of the energy is always lost. Explain why this is a true statement and identify the unusable or lost energy. [This was from my son’s sixth-grade science homework; your answer should refer to a law of thermodynamics and explain why it’s relevant.]

#29 Hint: 2nd law. Irreversibility


Answer 1

Spontaneous process are considered to be irreversible in nature since they lead to increase of entropy of the zuniverse. According to 2nd law of thermodynamics, it is not possible to convert the entire heat obtained from hot object into useful work, rather some part of the heat energy has to be rejected to the surroundings, so as to maintain the entropy of the universe to be greater than or equal to zero.

The rejected (lost) heat causes rise of entropy of surroundings.