Chemical interactions and phase transformations are traditionally characterized by thermodynamic indicators and state diagram. Transformations of substances are followed by thermal effects and changes of volume. Density, important characteristic of substances, is result of two indicators: 1) the weight which is concentrated in atomic nuclei and 2) the volume which is formed by electron shells. Chemical processes are the reactions proceeding with formation of new connections. The act of chemical interaction consists in formation of new electronic (molecular) orbitals. The chemical bond between atoms is caused by overshoot of electronic clouds. Transformations of substances and formation of new structure is defined by interaction of electron shells of atoms and molecules. Thermal processes are rather in detail considered in numerous works on chemical thermodynamics, and information on changes of volumes is not enough.