second law of thermodynamics

describes: all manner of physical processes in such a way as to predict the direction in which they will proceed spontaneously.

can be stated: in various ways, all of which are interrelated:

No process is possible whose sole result is the transfer of heat from a colder to a hotter body.
No process is possible in which the sole result is the transfer of heat from a body and its complete conversion into work.
No process is possible that would lead to a net decrease in the entropy of the Universe,
Any spontaneous process is irreversible and leads to an increase in the entropy of the Universe.