• Main definitions
• Ideal Gas
• The three laws of thermodynamic
• Heat Engines

Ideal gas law and thermodynamic processes.

An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly eleastic 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 and is called the Ideal Gas Law(or equation of state)

• n = number of moles
• V=volume
• T=absolute temperature
• P=absolute pressure
• R = universal gas constant = 8.3145 J/mol K
• N = number of molecules
• k = Boltzmann constant = 1.38066 x 10^-23 J/K = 8.617385 x 10^-5 eV/K
• k = R/N_A
• N_A = Avogadro's number = 6.0221 x 10²³

If we know the equation of state then we could calculate states of simplest systems, for that we need to know only two independent variables of three Đ = f1 (v, ň); v = f2 (Đ, Ň); Ň = f3 (v, Đ)
Thermodynamic processes are often shown on plots of the states where state variables laid off on the axis. Points on the plain of this plot are matching some state of the system, and lines are thermodynamic processes which are shifting system from one state to another.
Here are these processes.
For a constant temperature process involving an ideal gas, pressure can be expressed in terms of the volume(this process is called isothermal):

For a constant pressure process involving an ideal gas, volumecan be expressed in terms of the temperature(this process is called constant pressure process):

For a constant volume process involving an ideal gas, pressure can be expressed in terms of the temperature(this process is called constant volume process):

If there is no heat transfer between the material body and enviroment such processes are called adiobatic. This is idealization in real world there are no such processes but some fast processes are considered as adiobatic.