Molecular physics and thermodynamics are the branches of physics that study macroscopic processes in bodies that are associated with a large number of atoms and molecules contained in them.
Molecular physics studies the structure and properties of substances from the side of molecular kinetic representations, which are based on the fact that any body consists of molecules (particles) in constant chaotic motion. Molecular physics studies the processes of the combined effects of a colossal number of molecules.
Thermodynamics studies the general properties of a (macroscopic) system in thermodynamic equilibrium.
The study of macroscopic processes is carried out using two methods:
1. molecular - kinetic (molecular physics is based on this method);
2. thermodynamic, underlies thermodynamics.
These methods complement one another.
Molecular physics is based on the molecular-kinetic theory, according to which the structure and properties of bodies are explained by the chaotic movement and interaction of molecules, atoms and ions (i.e. particles). Experienced properties of bodies (for example, pressure) are explained by the effect of particles, that is, the properties of the entire macroscopic system depend on the properties of the particles, the characteristics of their motion and the averaged values of the dynamic characteristics of the particles. It is not possible to determine the exact location of a particle in space and its momentum, however, their huge number makes it possible to efficiently use the molecular-kinetic (statistical) method, since there are certain patterns in the behavior of average parameters.
The main provisions of the molecular-kinetic theory are:
1. Any substance consists of particles - molecules and atoms, and those of smaller particles;
2. Molecules, atoms and other particles are in a continuous chaotic motion;
3. Between the particles there is an attractive force and a repulsive force.
Molecular physics considers: the structure of gases, solids and liquids, their change under external influence (pressure, temperature, magnetic and electric fields), transport phenomena (internal friction, thermal conductivity, diffusion), phase transition processes (evaporation and condensation, crystallization and melting etc.), phase equilibrium, critical state of substances.
Thermodynamics studies thermal processes that are associated with changes in body temperature and its state of aggregation. Thermodynamics does not consider microprocesses, it is engaged in establishing the relationships existing between the macroscopic properties of substances. A thermodynamic system is a collection of macroscopic bodies interacting and exchanging energy between themselves and with the external environment. The task of the thermodynamic method is to determine the state in which the thermodynamic system is located at any time. The set of physical properties characterizing the properties of the system (pressure, temperature, volume), determine its state.
Thermodynamic process - a change in the thermodynamic system associated with a change in its parameters.
Molecular chemistry is the science of the composition, structure, and physical properties of a substance.
Physical properties of substances:
1. state of aggregation (solid, gas, liquid);
2. smell;
3. color;
4. density;
5. solubility;
6. electrical and thermal conductivity;
7. melting and boiling points.
Any substance consists of atoms and molecules, ions.
An atom is the smallest particle of matter, consisting of a positively charged nucleus and a negatively charged electron shell.
A positive charge carries a proton. The core also includes neutral elementary particles - neurons. The unit of negative charge is an electron.