Stoichiometry deals with the calculation of the mass and volume of reactants and products in chemical reactions. The term stoichiometry was first introduced by the German chemist Jeremias Benjamin Richter (1762-1807) in the late 19th century. It relates to the relative amounts of reactants and products in a chemical reaction. His calculations are based on the fact that atoms cannot be created or destroyed. The number and types of atoms before and after the reaction are always the same.
A phase diagram is a graph that is a representation of the phases present in a material at variations in temperature, pressure, and composition. This diagram is the basis of understanding for all heat treatment operations. In general, phase diagrams are constructed at equilibrium (the condition is very slow cooling). This diagram is used to identify and predict many aspects of material properties.