In the absence of electric or magnetic fields charged particles in weakly ionized gases participate in molecular collisions. Their motions follow closely the classical kinetic gas theory.

**CLASSICAL GAS LAWS**

In the
absence of electric or magnetic fields charged particles in weakly ionized
gases participate in molecular collisions. Their motions follow closely the
classical kinetic gas theory.

The
oldest gas law established experimentally by Boyle and Mariotte states that for
a given amount of enclosed gas at a constant temperature the product of
pressure (p) and volume (V) is constant or

pV = C =
const. 2.1

In the
same system, if the pressure is kept constant, then the volumes V and V_{0}
are related to their absolute temperatures T and T_{0} (in K) by
Gayâ€“Lussacâ€™s law:

When
temperatures are expressed in degrees Celsius, eqn (2.2) becomes;

Equation
(2.3) suggests that as we approach ÆŸ = -273Â°C
the volume of gas shrinks to zero. In reality, all gases liquefy before
reaching this value.

According
to eqn (2.2) the constant C in eqn (2.1) is related to a given temperature T_{0}
for the volume V_{0}:

The ratio
C_{0}/T_{0}_ is called the universal gas constant and is
denoted by R. Equation (2.5) then becomes

pV = RT =
C 2.6

Numerically
R is equal to 8.314 joules/Â°Kmol. If we take n as the number of moles, i.e. the
mass m of the gas divided by itâ€™s mol-mass, then for the general case eqn (2.1)
takes the form

pV = nC =
nRT, 2.7

Equation
(2.7) then describes the state of an ideal gas, since we assumed that R is a

constant
independent of the nature of the gas. Equation (2.7) may be written in terms of
gas density N in volume V containing N_{1} molecules.

Putting N
= N_{A} where N_{A} = 6.02 * 10^{23} molecules/mole, N_{A}
is known as the Avogadroâ€™s number. Then eqn (2.7) becomes

The
constant k = R/NA is the universal Boltzmannâ€™s constant (=1.3804 *10^{23}
joules/Â°K) and N is the number of molecules in the gas.

The
fundamental equation for the kinetic theory of gas is derived with the
following assumed conditions:

Â·
Gas consists of molecules of the same mass which
are assumed spheres.

Â·
Molecules are in continuous random motion.

Â·
Collisions are elastic â€“ simple mechanical.

Â·
Mean distance between molecules is much greater
than their diameter.

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High Voltage Engineering : Electrical breakdown is gases, solids& Liquids : Classical Gas Laws |

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