Short answers, pulled from the story.
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems using the principles, practices, and concepts of physics, such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics, and chemical equilibria. Unlike chemical physics, it is predominantly a supra-molecular science concerned with the bulk of materials rather than molecular or atomic structure alone.
Mikhail Lomonosov coined the term physical chemistry in 1752, when he presented a lecture course entitled a course in true physical chemistry before the students of Petersburg University. He defined it as the science that must explain, through physical experiments, the reason for what happens in complex bodies through chemical operations.
Modern physical chemistry originated in the 1860s to 1880s with work on chemical thermodynamics, electrolytes in solutions, chemical kinetics, and other subjects. A key milestone was the 1876 publication by Josiah Willard Gibbs of his paper On the Equilibrium of Heterogeneous Substances.
The main branches of physical chemistry include chemical thermodynamics, chemical kinetics, statistical mechanics, quantum chemistry, electrochemistry, photochemistry, surface chemistry, solid-state chemistry, and spectroscopy. Quantum chemistry applies quantum mechanics to chemical problems, while chemical kinetics studies which reactions occur and how fast.
Wilhelm Ostwald, Jacobus Henricus van 't Hoff, and Svante August Arrhenius were the leading figures in physical chemistry in the late 19th and early 20th centuries. All three were awarded the Nobel Prize in Chemistry between 1901 and 1909, and Ostwald and van 't Hoff founded the journal Zeitschrift für Physikalische Chemie in 1887.
Physical chemistry uses additive physicochemical property methods to calculate more than twenty properties, including boiling point, critical point, surface tension, and vapor pressure, from chemical structure alone, even for molecules that have not been synthesized. These approaches include the Group contribution method, the Lydersen method, the Joback method, Benson group increment theory, and the quantitative structure, activity relationship.