But Haber was not alone with his thoughts because the experimental origin
of the Third Law involved a number of physical chemists. By the early 1900s,
van’t Hoff, Nernst and the Americans Gilbert Lewis and Theodore W.
Richards had also concerned themselves with the problem of changes at
absolute zero. In 1902, whilst working on a different problem, Richards had
collected the heats and the free energies of a number of reactions as a function
of temperature. Unfortunately, Richards had a fundamental misunderstanding of thermodynamics and he was unable to ‘see’ what his data told him. But
just down the hall at Harvard’s chemistry department was Gilbert Lewis, a
competent thermodynamicist who had tackled the problem of the relationship between free energy and chemical equilibrium in his doctoral thesis,
which Richards had supervised but did not understand. Because he knew that
the free energy change determines the point of chemical equilibrium, Lewis
had proposed a general equation relating the two. Richards therefore had the
data and Lewis the understanding, but the two men had fallen out, Richards
accusing Lewis of ‘appropriating’ his data (in a separate area) and by 1904
Lewis left Harvard for the Philippines. There is no doubt that had Lewis seen
Richards’ data he would have spotted the ‘pattern’ and solved the problem.
But he was now ‘out of the loop’ and the field was left open to van’t Hoff,
Haber and Nernst. van’t Hoff’s stab at a solution postulated two possible
behaviours for the variation of the data with temperature, each missing the
‘obvious’ in the actual data. Haber’s approach to the problem developed an
over-complicated solution which, although probably quite correct, was difficult to prove.
Early in 1906 however, Nernst published his ‘Heat Theorem’ based on the
pattern in the experimental data that all the others had missed. Using reliable
published sources for his data, Richards had already noticed that as the
temperature fell, the change in the enthalpy and the free energy for a reaction
tended to converge to a some common value. At the time, this behaviour was
perfectly evident from a number of perspectives. For example, Eq. (2.1)
always applies, and in the limit as T tends to zero (T ! 0), the equation
becomes,
DG ¼ DH or ðDG À DHÞ ! 0
This is illustrated
48 very simply in the diagram below (Fig. 2.3);
Similarly, the Gibbs Helmholtz relation
47 ;
2 Fritz Haber and Karlsruhe
61
of the Third Law involved a number of physical chemists. By the early 1900s,
van’t Hoff, Nernst and the Americans Gilbert Lewis and Theodore W.
Richards had also concerned themselves with the problem of changes at
absolute zero. In 1902, whilst working on a different problem, Richards had
collected the heats and the free energies of a number of reactions as a function
of temperature. Unfortunately, Richards had a fundamental misunderstanding of thermodynamics and he was unable to ‘see’ what his data told him. But
just down the hall at Harvard’s chemistry department was Gilbert Lewis, a
competent thermodynamicist who had tackled the problem of the relationship between free energy and chemical equilibrium in his doctoral thesis,
which Richards had supervised but did not understand. Because he knew that
the free energy change determines the point of chemical equilibrium, Lewis
had proposed a general equation relating the two. Richards therefore had the
data and Lewis the understanding, but the two men had fallen out, Richards
accusing Lewis of ‘appropriating’ his data (in a separate area) and by 1904
Lewis left Harvard for the Philippines. There is no doubt that had Lewis seen
Richards’ data he would have spotted the ‘pattern’ and solved the problem.
But he was now ‘out of the loop’ and the field was left open to van’t Hoff,
Haber and Nernst. van’t Hoff’s stab at a solution postulated two possible
behaviours for the variation of the data with temperature, each missing the
‘obvious’ in the actual data. Haber’s approach to the problem developed an
over-complicated solution which, although probably quite correct, was difficult to prove.
Early in 1906 however, Nernst published his ‘Heat Theorem’ based on the
pattern in the experimental data that all the others had missed. Using reliable
published sources for his data, Richards had already noticed that as the
temperature fell, the change in the enthalpy and the free energy for a reaction
tended to converge to a some common value. At the time, this behaviour was
perfectly evident from a number of perspectives. For example, Eq. (2.1)
always applies, and in the limit as T tends to zero (T ! 0), the equation
becomes,
DG ¼ DH or ðDG À DHÞ ! 0
This is illustrated
48 very simply in the diagram below (Fig. 2.3);
Similarly, the Gibbs Helmholtz relation
47 ;
2 Fritz Haber and Karlsruhe
61