Question:easy
According to the second law, which of the following is impossible?
According to the second law, which of the following is impossible?
Show Hint
The Second Law essentially establishes that "you cannot break even." Some energy must always be degraded as low-grade heat during any cyclical conversion process.
Updated On: Jul 3, 2026
- Melting of ice at \( 0^\circ\text{C} \)
- \( 100\% \) conversion of heat to work
- Expansion of gas into a vacuum
- Reversible adiabatic expansion
Show Solution
The Correct Option is B
Solution and Explanation
Every real heat engine takes in heat from a hot source, converts part of it to useful work, and must dump the leftover heat into a cooler sink, it can never turn every last unit of heat into work with nothing wasted. If it could, we would have a machine running forever off a single heat reservoir with no waste, which the second law forbids outright. Ice melting at 0 degrees and gas expanding freely into empty space both happen naturally and raise the system's entropy, which the second law fully permits, and a reversible adiabatic expansion is an idealised but allowed process. So the one truly forbidden case here is turning heat completely into work.
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