Laws of Thermodynamics

“Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency” (Lord Kelvin). The four laws of thermodynamics were derived from the work of, among others, Sadi Carnot, Émile Clapeyron, Julius Mayer, Hermann Hess, und Rudolf Clausius. They explain heat exchange, entropy, and how substances and machines behave under energy transformation.

The four Laws of Thermodynamics:

0. (Zeroth) If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

1. The internal energy of an isolated system is constant. The law of conservation of energy is a consequence, and states that energy can be transformed from one form to another, but cannot be created or destroyed.

2. Heat cannot spontaneously flow from a colder location to a hotter location. Rudolf Clausius: There is no change in state, the only result of which is the transmission of heat from a body of a lower temperature to a higher temperature body. Entropy is a measure of the loss of order (distribution of energy) and tends to increase with time. This leads to the irreversibility of reactions.

3. As a system approaches absolute zero (0 K or −273.15 °C), all processes cease and the entropy of the system approaches a minimum value. Entropy can not be destroyed. However, entropy may arise in the system. Energy degradation results from irreversible processes.

Intensive quantities: temperature T, pressure ρ, concentration n, chemical potential μ

Extensive quantities: internal energy U, entropy S, volume V and particle number

N