State third law of thermodynamics. Give ‘two’ uses.

The third law of thermodynamics, also known as Nernst's theorem or the Nernst heat theorem, states that "the entropy of a pure crystalline substance approaches zero as the temperature approaches absolute zero (0 Kelvin or -273.15 degrees Celsius)."

Two uses of the third law of thermodynamics are:

Determining absolute entropies: The third law of thermodynamics provides a reference point for determining the absolute entropy of a substance at a given temperature. By measuring the entropy change of a substance relative to this reference point, it is possible to calculate the absolute entropy of that substance. This information is valuable in various fields, such as chemistry and materials science, where knowledge of the entropy of substances at different temperatures is essential for predicting and understanding their behavior.

Evaluating the feasibility of processes: The third law of thermodynamics is also employed to assess the feasibility of certain processes or reactions at low temperatures. It establishes the limiting conditions as temperature approaches absolute zero, enabling scientists and engineers to determine if a process can reach this lowest temperature or if it is thermodynamically prohibited. This understanding aids in designing and optimizing low-temperature systems, such as cryogenic applications and superconductors, where extremely low temperatures are involved.

These are just two examples of the numerous applications and implications of the third law of thermodynamics in various scientific and engineering domains.