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system is the functional dependence of the equilibrium pressure p in the
system on the volume and temperature:
p  f (V ,T )

1.4. Main Principles of Molecular-Kinetic Theory

The molecular-kinetic theory explains the obtained experimental data

(pressure, temperature, distribution of kinetic energy, Brownian
movement, heat capacity, objective law of molecule distribution on
velocities, transfer phenomena etc.) as the result of the motion and
interaction of a big number of molecules in the system. The theory is based

on the following three main statements:
1. All substances consist of the giant number of particles — molecules,
 10
atoms and ions. Linear sizes of these particles are of order 10 m.
2. Molecules (atoms and ions) are involved in the heat motion. The body
temperature determines the average kinetic energy of this motion.

3. The forces of interaction between molecules (atoms and ions) exist.
Depending on the distance between the particles these forces can be
attractive or repulsive.

1.5 Ideal Gas .Main Equation of Molecular-Kinetic Theory
of Ideal Gas

An ideal gas is defined as one in which all collisions between
atoms or molecules are perfectly elastic and in which there are no
intermolecular attractive forces. One can visualize it as a collection of

perfectly hard spheres which collide but which otherwise do not interact
with each other. In such a gas all the internal energy is in the form of
kinetic energy and any change in internal energy is accompanied by a

change in temperature. An ideal gas can be characterized by three state
variables: absolute pressure (P), volume (V), and absolute temperature
(T). The relationship between them may be deduced from kinetic theory

Kinetic theory enables to set relation between a macroscopic
quantities ( pressure p, volume V) and microscopic quantities by equation
that is called the main equation of molecular-kinetic theory of ideal gas
We are now ready to develop in detail the relation between the

kinetic-molecular model of an ideal gas and ideal-gas equation of state.
We consider a container of volume V, containing N identical molecules
with mass m each. We assume that each collision of a molecule with a

wall of the container is perfectly elastic, as shown in Fig.1.5.1. In each

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