The third law of thermodynamics, also known as Nernst's theorem or the Nernst heat theorem, is a fundamental principle in the field of thermodynamics. It addresses the behavior of systems as they approach absolute zero temperature (0 Kelvin or -273.15 degrees Celsius).
The third law of thermodynamics states that as the temperature of a system approaches absolute zero, the entropy of the system also approaches a minimum or zero value. In other words, the entropy of a perfect crystalline substance at absolute zero is zero.
Entropy is a measure of the disorder or randomness in a system. The third law implies that a perfectly ordered and crystalline substance, when cooled to absolute zero, will have no residual thermal energy or randomness. This means that all molecular motion ceases, and the substance is in its lowest possible energy state.
While the third law of thermodynamics sets a limit on the behavior of systems at extremely low temperatures, it is also useful in understanding the behavior of systems at higher temperatures. It provides a reference point for measuring entropy and allows for the calculation of absolute entropy values for different substances.
The third law of thermodynamics has significant implications in various fields, such as physics, chemistry, and material science. It helps explain phenomena like superconductivity, where electrical resistance disappears at extremely low temperatures, and it provides insights into the behavior of complex systems at the atomic and molecular level.