§2 MendeleevClapeyron equation
Every system can be in different states with different temperature, pressure, volume, etc.
The values ??of p, V, T, and others characterize the state of the system, called the parameters of the state.
If any of the parameters within the system varies from point to point, a condition called nonequilibrium. If the system parameters are the same at all points under constant external conditions, such a state is called equilibrium.
Any process,
ie transition from one state to another is related to an imbalance of
the system. But infinitely slow process will consist of a sequence of
equilibrium states. This process is called equilibrium. At sufficiently
low flow real processes can approach to equilibrium. Equilibrium
process is reversible, that is, the system goes from state 1 to state 2
and from 2  1, passing through the same intermediate states.
The process by
which the system, having a number of intermediate states, returns to
its original state is a round or cycle process: the process of
12341 in the figure.
Relationship between the parameters of the state called the state equation:
f (p, V, T) = 0
Clapeyron, using the laws of Boyle and Charles led the ideal gas equation.
1 – 1’: T = const – BoyleMariotte law:
p_{1}V_{1} = p_{1}’ V_{2};
1’ – 2: V = const – Charles law
because states 1 and 2 are chosen arbitrarily, for a given mass of gas quantity is constant
 Clapeyron equation
B  gas constant, is different for different gases.
Mendeleev Clapeyron equation combined with the law of Avogadro
 for 1 mole
V_{m}  molar volume
MendeleevClapeyron equation
R  universal (molar) gas constant
p = const; :
The physical meaning of R: is numerically equal to the work done by the gas during the isobaric (p = const) heating one mole of gas (m / μ = ν = 1) by one Kelvin (ΔT = 1 K)
We introduce the Boltzmann constant
then
p 
pressure of an ideal gas at a given temperature is directly
proportional to the concentration of the molecules (or gas density). At
the same p and T, all gases contain in unit volume the same number of molecules.
n  concentration of molecules (number of molecules per unit volume). The number of molecules under normal conditions in 1 m^{3} called the number Loschmidt:
§ 3 The basic equation of the molecularkinetic theory (m.k.t.) gases.
At
random motions of gas particles collide with each other and with the
walls of the vessel. The mechanical action of the collision, the vessel
is seen as pressure on the walls. We distinguish on wall of the vessel
some elementary area ΔS and find the pressure on this area.
The momentum obtained by concerned wall by the impact of a single molecule will be equal
m_{0}  mass of a single molecule.
Newton's second law can be written as:
Δt_{i}time between two successive collisions of the ith molecule with this wall
All directions are equivalent:
We introduce the mean square velocity, which characterizes the whole set of molecules
Pressure
 the basic equation of the MKT
From equation Mendeleev  Clapeyron:
