Principal concepts of physical chemistry useful in steel making are;

System: - It is a group of bodies which interact with each other and can be isolated, either mentally or physically, from the surroundings Ex. Metal-slag systems.
    A system composed of a number of portions, possessing different properties separated from one another by interfaces is called heterogeneous. If there are no such interfaces in a system, it is called homogenous.

Phase: - It is combination of all the homogenous portions of a system, which have the identical compositions and properties and are separated by interfaces from the other portions.
    A process is characterized by process parameters, i.e. by variations in a system associated with changes in its parameters of state; steel making process usually takes place at nearly constant pressure, i.e. are essentially isobaric. For that reason, the thermodynamic calculations of steelmaking processes are based on using the variations in the isobaric-isothermal potential G, enthalpy H and the thermal effect Qp.
     Physico-chemical phenomena can be studied both by direct experimenting and on the basis of theoretical findings and generalizations made in the neighboring branches of science. The existing control techniques can give ample information on the parameters of a steelmaking heat. This information can be analysed by using the laws of physical chemistry to obtain the following data:
1.The direction in which a process or a reaction will occur, and the final products which will be obtained.
2.The characteristics of the final state of the system; the ranges of certain parameters within which a particular process can occur, and the state of the system at the end of the process.
3.The rate of the process and its dependence on various parameters.