The molecular physics studies change of properties of substances at the molecular level depending on their aggregate state (firm, liquid and gaseous). This section of physics is very extensive and includes a set of subsections.
Instruction
1. First of all, the molecular physics studies the structure of a molecule and substances in general, its weight and the size, and interaction of its making microscopic particles (atoms). This subject includes studying relative molecular weight (the relation of mass of one molecule / atom of substance to a constant – the mass of one atom of carbon); concept of amount of substance and molar weight; expansion/compression of substances at heating/cooling; speeds of motion of the molecules (molecular and kinetic theory). The molecular and kinetic theory is based on studying separate molecules of substance. And in a subject of behavior of substance at various temperatures very interesting phenomenon is considered – much know that when heating substance extends (the distance between molecules increases), and when cooling contracts (the distance between molecules decreases). But here that interestingly – upon transition of water from a condition of liquid in a firm phase (ice), water extends. It is provided with polar structure of molecules and hydrogen communication between them, still so unclear to modern science.
2. Also, in molecular physics there is a concept of "ideal gas" - it is the substance which is in a gaseous form and having certain properties. Ideal gas is very discharged, i.e. its molecules do not interact among themselves. In addition, ideal gas submits to laws of mechanics while real-life gases have no such property.
3. From the section of molecular physics the new direction – thermodynamics appeared. This section of physics considers the structure of substance and influence on it of external factors, such as pressure, volume and temperature, disregarding a microscopic picture of substance, and considering communications in it in general. If to read textbooks in physics, it is possible to encounter special schedules of dependence of these three sizes in relation to a condition of substance – they represent isochoric (volume is invariable), isobaric (pressure is invariable) and isothermal (temperature is invariable) processes. The concept of thermodynamic balance also enters thermodynamics – when all three of these sizes are constant. Very interesting question which is raised by thermodynamics – why, for example, water at a temperature of 0 °C can is both in liquid, and in strong aggregate state.