how many of different sorts of molecules determines the rate of the chemical
reaction. His introduction of the terms such as unimolecular, and bimolecular
reaction, was of far-reaching importance for the future development of the theory of
reaction mechanisms.
Wilhelm Friedrich Philipp Pfeffer (1845–1920) has systematically measured
osmotic pressure, the force that appear in systems in which two solutions of different concentrations are separated with the semipermeable membrane. The solution
with higher concentration induces pressure on the membrane in direction to the
solution with lower concentration. Stimulated with the Pfeffer’s measurements,
van’t Hoff has demonstrated that the ratio between concentration and the osmotic
pressure is analogous to the ratio of the volume and pressure of ideal gas. Thus, his
law of osmotic pressure is analogous to the Boyle-Mariott law of ideal gas.
Harmon Northrop Morse (1848–1920) has extended van’t Hoff’s law for all,
organic and inorganic solutions. However, this extension has in the equation an
additional factor i that was an empirical parameter. Since it was not possible to
calculate the factor i, the Morse equation is semiemprical, i.e. its solution depends
on the parameters provided exclusively from the observations. Semiempiria, the
improvement of equations by addition of some parameters obtained by experience,
became in this way part of epistemology, and this method will play very important
role in the development of methods of calculations of molecular structures. On the
other hand, the theories that are based on the “fundamental truth”, i.e. on the
heuristic statements, so called ab initio theories, are in reality out of use because
their calculi are highly complex. Science, and especially chemistry, has developed
its epistemology that is basically semiempiric.
Although, at the first sight, is seems that the semiempirical character of science is
a signal for its weakness, it should be pointed out that the introduction of experienced parameters in calculations represents a germ of new theoretical extensions.
Discussion about the Morse factor i has initiated new discovery for which the
most of the credit should be given to Svante August Arrhenius (1859–1927). In
the year 1887 Arrhenius has created the theory about the electrolytic dissociation:
acids, bases, and salts are in water solution partially separated in anions and cations.
From the ratio of concentrations of ions and nondissociated molecules (the extent of
dissociation) Arrhenius has calculated the factor i. Thus, semiempirical addition to
theory has initiated its extension to new theory in which this semiempirical factor
acquires unequivocal physical meaning. This interplay between introducing and
vanishing of semiempirical entities is one of central forces in the development
of science.
Arrhenius idea about the equilibrium of dissociated and non-dissociated molecules was generalized in the law of dilution discovered by Friedrich Wilhelm
Ostwald (1853–1932) , the Nobel laurate for the year 1909, and in the law of
chemical equilibrium formulated by Peter Waage (1833–1900) and Cato Maximilian Guldberg (1836–1902).
The discovery that the disturbed system always has a tendency to be equilibrated, which is in chemistry known as Le Châtelier principle (Henry Louis Le
11 Models and Reality
109
reaction. His introduction of the terms such as unimolecular, and bimolecular
reaction, was of far-reaching importance for the future development of the theory of
reaction mechanisms.
Wilhelm Friedrich Philipp Pfeffer (1845–1920) has systematically measured
osmotic pressure, the force that appear in systems in which two solutions of different concentrations are separated with the semipermeable membrane. The solution
with higher concentration induces pressure on the membrane in direction to the
solution with lower concentration. Stimulated with the Pfeffer’s measurements,
van’t Hoff has demonstrated that the ratio between concentration and the osmotic
pressure is analogous to the ratio of the volume and pressure of ideal gas. Thus, his
law of osmotic pressure is analogous to the Boyle-Mariott law of ideal gas.
Harmon Northrop Morse (1848–1920) has extended van’t Hoff’s law for all,
organic and inorganic solutions. However, this extension has in the equation an
additional factor i that was an empirical parameter. Since it was not possible to
calculate the factor i, the Morse equation is semiemprical, i.e. its solution depends
on the parameters provided exclusively from the observations. Semiempiria, the
improvement of equations by addition of some parameters obtained by experience,
became in this way part of epistemology, and this method will play very important
role in the development of methods of calculations of molecular structures. On the
other hand, the theories that are based on the “fundamental truth”, i.e. on the
heuristic statements, so called ab initio theories, are in reality out of use because
their calculi are highly complex. Science, and especially chemistry, has developed
its epistemology that is basically semiempiric.
Although, at the first sight, is seems that the semiempirical character of science is
a signal for its weakness, it should be pointed out that the introduction of experienced parameters in calculations represents a germ of new theoretical extensions.
Discussion about the Morse factor i has initiated new discovery for which the
most of the credit should be given to Svante August Arrhenius (1859–1927). In
the year 1887 Arrhenius has created the theory about the electrolytic dissociation:
acids, bases, and salts are in water solution partially separated in anions and cations.
From the ratio of concentrations of ions and nondissociated molecules (the extent of
dissociation) Arrhenius has calculated the factor i. Thus, semiempirical addition to
theory has initiated its extension to new theory in which this semiempirical factor
acquires unequivocal physical meaning. This interplay between introducing and
vanishing of semiempirical entities is one of central forces in the development
of science.
Arrhenius idea about the equilibrium of dissociated and non-dissociated molecules was generalized in the law of dilution discovered by Friedrich Wilhelm
Ostwald (1853–1932) , the Nobel laurate for the year 1909, and in the law of
chemical equilibrium formulated by Peter Waage (1833–1900) and Cato Maximilian Guldberg (1836–1902).
The discovery that the disturbed system always has a tendency to be equilibrated, which is in chemistry known as Le Châtelier principle (Henry Louis Le
11 Models and Reality
109