The Four Laws of Thermodynamics

0. About thermal equilibrium
If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

1. About the conservation of energy
The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to or removed from the system and teh work done on or about the system. So, we can say (1) “Energy is neither created nor destroyed.”

2. About entropy
The total entropy of any isolated thermodynamic system always increases over time, approaching a maximum value or we can say, “In an isolated system, the entropy never decreases.” Another way to phrase this: Heat cannot spontaneously flow from a colder location to a hotter area— work is required to achieve this.

3. About the absolute zero of temperature
As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: “the entropy of all systems and of all states of a system is smallest at absolute zero” or equivalently, “it is impossible to reach the absolute zero of temperature by any finite number of processes.” Absolute zero, at which all activity would stop if it were possible to happen, is -273.15°C, or -459.67°F, or 0K.