Nernsts Hypothesis for Condensed Systems

It is clear from the figure that the A and Q curves might differ appreciably even at temperatures very close to the absolute zero. We know from experiment, however, that BertheloFs principle of the equality of A and Q is generally approximately correct at moderately low temperatures. For this reason Nernst assumed that the A and curves have a common tangent at the absolute zero, so that 

We can derive several relationships from this fundamental equation of the theorem. 

These conclusions are, however, valid only for solid or (supercooled) liquid substances which can be cooled to the absolute zero without change of state, for only then do f T) and (T) remain continuous down to the absolute zero. For reactions between solids and liquids, therefore, the integration constant C is zero, and the reaction involves no change in entropy or in specific heat. 

Let us assume that the specific heats of all the reacting substances can be expanded in a power series. Their sum / (T)=--2Cj, can then also be wHtten as a power series, and we obtain f T) = a+f T -yT +.  

if the coefficients and y are positive, Qp increases while A diminishes with the temperature. If we are justified 

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