Kinetic theory of molecules is a classical microscopic statistical theory that studies the properties and laws of thermal motion of matter.It believes that material is composed ofmolecule、atom(hereinafter referred to as molecules). These molecules are in the process of non-stop and irregular thermal movement. There is an interaction between molecules, and the movement of molecules followsNewton's law of motion。It establishes the relationship between the macroscopic quantity and the corresponding microscopic quantity average through the method of statistical average of a large number of molecules to quantitatively explain the equation of state, thermodynamic properties and microscopic essence of diffusion, heat conduction, viscosity, etc. of objects.Molecular kinetic theory is mainly applied to gases, also known asKinetic theory of gas。[1]
set upAvogadro constantbyNA, the volume of the object isV, quality ism, density isρ，moleVolume isVmol, molqualityamountbyM, molecular volume isVzero, molecular weight ismzero, the number of molecules isn。
(3) Molecular volume of solid and liquidVzeroAnd diameterd
Vzero=Vmol/NA=M/ρNA=1/6πdthree，
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Kinetic theory of gas molecules
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People move from moleculesMicroscopic modelStart by giving some simplifiedassume, combinedprobability theoryandstatistical mechanicsAnd put forward kinetic theory of gases, which is mainly as follows:
(1) Gas is composed of molecules, which are very smallparticle, the distance between each other is greater than the diameter of the molecule (10-10m) It is much larger, and the molecular volume can be slightly neglected compared with the gas volume.
(2) Gas molecules are in permanent state in all directions at different speedsIrregular motioninTypical examples areDiffusion phenomenon、Brownian motion(All are indirect).The surface of Brownian motion reflects the irregular motion of macro particles, which actually reflectsmicrocosmicIrregular movement of molecules.
(3) Except in mutualcollisionThe interaction between gas molecules is weak, even negligible.
(4) Gas molecules collide with each other or with the wallElastic collision。
(5) The average kinetic energy of molecules andthermodynamicsThe temperature is proportional.
(6) There are interactions between molecules at the same time.Gravitation andrepulsionThe gravitational and repulsive forces decrease with the increase of the distance between molecules (the larger the molecular distance, the smaller the gravitational and repulsive forces; the smaller the molecular distance, the greater the gravitational and repulsive forces).However, the change of repulsion is faster than that of gravity, which actually shows the combined force of gravity and repulsion.Resultant force at 0~rIt shows repulsion whenr~Appears as gravity when ∞（rIs that gravity is equal to repulsioncritical point）。
