Second Law of Thermodynamics
The second law states that an Isolated thermodynamic system will never undergo a decrease in entropy.
It is important to note that a non-isolated system can decrease in entropy, but this will always result in a larger increase in entropy elsewhere. Equality occurs only for a reversible process.
Kelvin-Planck version
It can be shown that the second law is equivalent to the statement
It is impossible to construct a Heat engine operating in cycles that extracts heat from a reservoir and delivers an equal amount of work
or, equivalently
See also Thermal efficiency of a heat engine.
This is because a heat engine converts random energy of particle motion into ordered motion associated with mechanical work, a process analogous to unscrambling an egg.1
Footnotes
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2020. Essential university physics, p. 346 ↩