Second law of thermodynamics

Second law of thermodynamics can be defined in many ways, but the fundamental meaning of it is that "an isolated system will always spontaneously proceed towards the state of thermodynamic equilibrium where the entropy of the system is greater than in the previous state". This can also be explained in numerous other ways, for example

1. Heat won't spontaneously move from colder to warmer
2. It is impossible to create a device which would transfer heat completely to mechanical work
3. In an isolated system irreversible processes increase the entropy while reversible processes keep the entropy constant
4. Entropy of the universe increases
5. Isolated system proceeds to thermal equilibrium
6. Device that changes heat into mechanical work will always cause changes in the environment
7. Energy of the universe is constant
8. In an equilibrium a large system is in the macrostate that has the greatest multiplicity
9. Multiplicity tends to increase toward the maximum value