Physical chemistry is the study of macroscopic, atomic, subatomic and particle phenomena in chemical systems in terms of principles, practices and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, Analytical dynamics and chemical equilibrium. Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a macroscopic or supra-molecular science, since most of the principles on which it was founded are related to mass and not just to molecular structure / Atomic, chemical equilibrium and colloids).
One of the key concepts of classical chemistry is that all chemical compounds can be described as groups of atoms linked together and chemical reactions can be described as the making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they come together is one of the main objectives of physical chemistry. To describe atoms and bonds precisely, it is necessary to know where the nuclei of atoms are and how the electrons are distributed around them.
Quantum chemistry, a subfield of physical chemistry that deals especially with the application of quantum mechanics to chemical problems, provides tools to determine how strong and how the bonds are, how the nuclei move, and how light can Be absorbed or emitted by a chemical compound. Spectroscopy is the related sub-discipline of physical chemistry that deals specifically with the interaction of electromagnetic radiation with matter.
Another set of important issues in chemistry refers to what kind of reactions can occur spontaneously and what properties are possible for a given chemical mixture. This is studied in chemical thermodynamics, which establishes limits on quantities such as how much a reaction can proceed, or how much energy can be converted into work in an internal combustion engine, and which provides bonds between properties such as coefficient of thermal expansion and Rate of change Entropy with pressure for a gas or a liquid. It can often be used to assess whether a reactor or engine design is feasible, or to verify the validity of the experimental data. However, classical thermodynamics mainly refers to systems in equilibrium and reversible changes and not what actually happens, or speed, away from equilibrium.
