l. Clausius (l822-l888) It is impossible that, at the end of a cycle of changes, heat has been transferred from a colder to a hotter body without at the same time converting a certain amount of work into heat.
2. Lord Kelvin (l824-l907) In a cycle of processes, it is impossible to transfer heat from a heat reservoir and convert it all into work, without at the same time transferring a certain amount of heat from a hotter to a colder body.
3. Ludwig Boltzmann (l844-l906) For an adiabatically enclosed system, the entropy can never decrease. Therefore, a high level of organization is very improbable.
4. Max Plank (l858-l947) A perpetual motion machine of the second kind is impossible.
5. Caratheodory (l885-l955) Arbitrarily near to any given state there exist states which cannot be reached by means of adiabatic processes.
(From Sears and Zemansky): 100% conversion of heat into mechanical work is not possible by any form of engine. (p. 342) There is a tendency in nature to proceed toward a state of greater molecular disorder. This one-sidedness of nature produces irreversible processes. (p. 347)
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