Short answers, pulled from the story.
Mikhail Lomonosov defined physical chemistry as the science explaining the reasons for what happens in complex bodies through chemical operations using the provisions of physical experiments. He declared this definition before the students of Petersburg University on the 1st of March 1752. This definition bound the study of matter to the laws of motion and moved the field from observation to explanation.
Josiah Willard Gibbs published a dense paper titled On the Equilibrium of Heterogeneous Substances in 1876. This work introduced concepts including Gibbs energy, chemical potentials, and the phase rule. It established the mathematical limits of what could happen in reactions and defined how much energy could be converted into work.
Wilhelm Ostwald, Jacobus Henricus van 't Hoff, and Svante August Arrhenius received the Nobel Prize in Chemistry between 1901 and 1909. These three men were the leading figures of physical chemistry in the late 19th century. They also founded the first scientific journal dedicated to the field, Zeitschrift für Physikalische Chemie, in 1887.
Linus Pauling used the principles of quantum chemistry to determine the strength and shape of chemical bonds in the 1930s. This application allowed scientists to see how electrons were distributed around nuclei and how light could be absorbed or emitted by a compound. The development of spectroscopy techniques such as infrared spectroscopy and nuclear magnetic resonance spectroscopy supported these theoretical advances.
The Avogadro constant is 6 times 10 to the 23rd power particles. Statistical mechanics explains the behavior of mixtures containing this number of particles by predicting properties from molecular properties without relying on empirical correlations. This field serves as the bridge between the microscopic world of individual atoms and the macroscopic world of bulk matter.
Algorithms such as the Lydersen method, the Joback method, and the Benson group increment theory allow scientists to calculate more than 20 physicochemical properties from chemical structure alone. These methods predict boiling points, critical points, surface tension, and vapor pressure with remarkable accuracy. This predictive capability has transformed physical chemistry into a field where properties can be known before a substance is synthesized.