The Third Law of Thermodynamics

The Third law of Thermodynamics strives to characterize the low-temperature behavior of a system. O ne way of interpreting the meaning of the third law is:

"It is impossible to reduce the temperature of a system to absolute zero (0°Kelvin) in a finite number of reversible steps"

The Third Law

The Principle of Thomsen and Berthelot Development of this characterizing principle began in 1906 with Walther Nernst, a chemist from Germany. Nernst developed the "New Heat Theorem" which states: as 0°Kelvin / absolute zero is approached, the change in entropy for a transformation of a system becomes zero. Mathematically, this is,

[math]\displaystyle{ \lim_{T \to 0} \Delta S = 0 }[/math]

Nernst developed two different ways of stating the third law, which could be described as entropy change, and unattainability.

Max Planck proposed a different approach, which would ultimately end up becoming a stronger statement for stating the third law of thermodynamics.His statement can be described as absolute entropy.

Through experimental analysis, Julius Thomsen and Marcellin Berthelot developed a self named principle, stating: chemical changes, which always produce heat, follow a path that leads to maximizing the expulsion of heat / minimizing the chemical/physical systems energy.

In a system, the heat absorbed 'Q' can be described as:

[math]\displaystyle{ Q = (E_f+P_oV_f)-(E_i+P_oV_i) }[/math]

[math]\displaystyle{ = H_f - H_i }[/math]

[math]\displaystyle{ = ΔH }[/math]

This tells us that Enthalpy is equivalent to the heat absorbed 'Q'. Connecting this to the principle of Thomsen and Berthelot tells us that a system will seek a state that minimizes its enthalpy.

The Stability Criteria for Gibbs free energy can be described as:

[math]\displaystyle{ G= E+PV-TS }[/math]

[math]\displaystyle{ dG= d[E+PV-TS] }[/math]

[math]\displaystyle{ dG_PT \lt 0 }[/math]

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