“Nernst heat theorem”的意思、由来-开放百科全书

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Nernst heat theorem

释义

The theorem
See also
References and notes
Further reading
External links

The Nernst heat theorem was formulated by Walther Nernst early in the twentieth century and was used in the development of the third law of thermodynamics.

The theorem

The Nernst heat theorem says that as absolute zero is approached, the entropy change ΔS for a chemical or physical transformation approaches 0. This can be expressed mathematically as follows:

The above equation is a modern statement of the theorem. Nernst often used a form that avoided the concept of entropy.^[1]

Another way of looking at the theorem is to start with the definition of the Gibbs free energy (G), G = H - TS, where H stands for enthalpy. For a change from reactants to products at constant temperature and pressure the equation becomes .

In the limit of T = 0 the equation reduces to just ΔG = ΔH, as illustrated in the figure shown here, which is supported by experimental data.^[2] However, it is known from thermodynamics that the slope of the ΔG curve is -ΔS. Since the slope shown here reaches the horizontal limit of 0 as T → 0 then the implication is that ΔS → 0, which is the Nernst heat theorem.

The significance of the Nernst heat theorem is that it was later used by Max Planck to give the third law of thermodynamics, which is that the entropy of all pure, perfectly crystalline homogeneous materials is 0 at absolute zero.

References and notes

1. ^{{cite book | last = Nernst | first = Walther | title = The New Heat Theorem | publisher = Methuen and Company, Ltd | year = 1926 | pages = }}- Reprinted in 1969 by Dover - See especially pages 78 – 85
2. ^{{cite book | last = Nernst | first = Walther | title = Experimental and Theoretical Applications of Thermodynamics to Chemistry | publisher = Charles Scribner's Sons | year = 1907 |location = New York | pages = 46| url = https://books.google.com/books?id=sYsJAAAAIAAJ&printsec=frontcover&dq=Walther+nernst}}- The labels on the figure have been modified. The original labels were A and Q, instead of ΔG and ΔH, respectively.

External links

Nernst heat theorem

Nernst-Theorem

2 : Thermochemistry|Walther Nernst

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The theorem

See also

References and notes

Further reading

External links