NERNST-SIMON STATEMENT:

The entropy change associated with any isothermal reversible process of a condensed system approaches zero.

Another statement of third law can be given like this:

It is impossible by any procedure, no matter how idealized, to reduce the entropy of a system to zero point value in a finite number of operations.

Physical and chemical facts which substantiate the third law:

1. For any phase change that takes place at low temperature, Clausius-Clayperon equation hold good,

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   From third law of thermodynamics, , since v_f - v_i is not zero. It shows that

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   This is substantiated by all known sublimation curves.

   
   Fig. 1.41 The temperature dependence of the change in the Gibbs function and in the enthalpy for an isobaric process

2. ΔG = ΔH - TΔs

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   At low temperature, TΔS is very small.

   ∴ ΔG = ΔH

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   Which confirms that .

3. From the Gibbs-Helmholtz equation

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    (Fig. 1.41)

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   Similarly, using Gibbs Helmholtz equation containing U and F

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   ∴ Cp = Cv = 0 as T → 0

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