Every phenomenon that occurs in the world of chemistry which requires the knowledge of physical concepts of motion, force and time is studied falls under the domain of physical chemistry. When scientists discuss about the nature of the forces that occur between the constituents of atoms or even intermolecular forces, they are all bound to the principles of physical chemistry and have to be consistent with them. It is actually a very broad branch of chemistry and it covers several different aspects which may or may not be related to each other.
Chemical thermodynamics is an important aspect of physical chemistry. It helps a chemist to answer questions such as how much of a reaction will go to completion and yield the product or how much of energy, which is released from the combustion of fuel, can be converted into useful work. More importantly, chemical thermodynamics is concerned with the nature of reactions which have achieved an equilibrium. At such a stage, there is no more reaction taking place and no more of the reactants are converting to form products. The laws of chemical thermodynamics have been devised to study a reaction system in such a state.
Chemical kinetics is yet another important part of physical chemistry and it helps anyone with proper knowledge to predict the rate of a chemical reaction. When you are conducting a reaction, it is always important to know how fast or how slow the reaction will proceed. For example, if there is a reaction which takes place spontaneously and the energy that is evolved in such a short duration causes an explosion, you would use chemical kinetics principles to investigate the rate and suggest ways to decrease it so that the reaction can proceed in a controlled manner without any explosions.
Physical chemistry is very much concerned with the physical forces that act between the particles of matter. Surface chemistry is a sub-branch of physical chemistry which deals with the interplay of forces between two chemical substances and the reactions that take place right where the two surfaces meet. An important example of surface chemistry would be the conversion of alkene to alkanes in a process called hydrogenation. In such a case the alkene is adsorbed over the surface of a catalyst such as palladium and hydrogens are supplied to it so that it can become a “saturated hydrocarbon.” A saturated hydrocarbon is one which has no multiple bonds just like an alkane.
Quantum chemistry is a relatively new branch of physical chemistry which is in particular concerned with the behavior of microscopic matter instead of macroscopic objects. Traditionally, physical chemistry has been concerned with the macroscopic entities only but quantum chemistry has attained a special place since it was observed that microscopic matter behaves differently from their bigger counterparts and same principles cannot be applied to both. Quantum chemistry aims to define the principles which govern the nature of atoms and form a model which can help us provide a reason for all the observations concerning it.