Zeroth Law of Thermodynamics
It states that if two bodies are each in thermal equilibrium with some third body, then they are also in equilibrium with each other.
Thermal equilibrium means that when two bodies are brought into contact with each other and separated by a barrier that is permeable to heat, there will be no transfer of heat from one to the other.
First Law of Thermodynamics
It states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy.
This means that heat energy cannot be created or destroyed. It can, however, be transferred from one location to another and converted to and from other forms of energy.
Second Law of Thermodynamics
It states that the state of entropy of the entire universe, as an isolated system, will always increase over time.
The second law also states that the changes in the entropy in the universe can never be negative.
The third law of thermodynamics
It states that the entropy of a perfect crystal at a temperature of zero Kelvin (absolute zero) is equal to zero.