The
kinetic gas equation is given as:
PV = 1/3 mnc2
P =
pressure
V = volume
M = mass
of molecule
n = no. of
molecules present in the given amount of gas
c = root
mean square speed.
Kinetic
energy for one mole of gas is given as c = c1 + c2 + … +
cn /n
The average kinetic energy per molecule is = average K.E per mole / NA
The average kinetic energy per molecule is = average K.E per mole / NA
= 3/2 RT/NA = 3/2 kT
Where k = R/NA and is known as the Boltzmann
constant.The total kinetic energy for 1 mol of the gas is
Etotal = NA.= 3/2 RT
Deduction of gas laws
from kinetic gas equation:
The ideal gas laws can be derived from the
kinetic theory of gases which is based on the following two important
assumptions:
i. The volume occupied by the molecules is negligible in comparison to the total volume of the gas
ii. The molecules exert no forces of attraction upon one another.
1. Deriving Boyle’s law:
From kinetic theory
PV = 1/3 mnc2
At constant temperature and at fixed amount of gas, c is constant.
Therefore, PV = constant ... Boyle’s law
2. Deriving Charle’s law:
PV = 1/3 mnc2
At constant pressure and amount,
V ∝ c2
∵ c2 ∝ T
∴ V ∝ T ... Charle’s law
3. Deriving Gay Lussac’s law:
PV = 1/3 mnc²
At constant volume and amount of gas
P ∝ c²
∵ c² ∝ T
∴ P ∝ T
i. The volume occupied by the molecules is negligible in comparison to the total volume of the gas
ii. The molecules exert no forces of attraction upon one another.
1. Deriving Boyle’s law:
From kinetic theory
PV = 1/3 mnc2
At constant temperature and at fixed amount of gas, c is constant.
Therefore, PV = constant ... Boyle’s law
2. Deriving Charle’s law:
PV = 1/3 mnc2
At constant pressure and amount,
V ∝ c2
∵ c2 ∝ T
∴ V ∝ T ... Charle’s law
3. Deriving Gay Lussac’s law:
PV = 1/3 mnc²
At constant volume and amount of gas
P ∝ c²
∵ c² ∝ T
∴ P ∝ T
Deriving Avogadro’s Maxwell showed that the average kinetic energies of molecules are equal at the same temperature, that is:
½ [m1c12] = kT = ½ [m2c22] and so [m1c12] = [m2c22]
But P1V1 = 1/3 [m1n1c12] and P2V2 = 1/3 [m2n2c22]
Now if P1 = P2 and V1 = V2, [m1n1c12] = [m2n2c22]
Therefore: n1 = n2 …… Avogadro’s law
5. Deriving Dalton's law of partial pressures:
For a mixture of gases:
PV = 1/3 ([m1n1c12] + 1/3 [m2n2c22] + …………)
P = 1/3 ([m1n1c12]/V + 1/3 [m2n2c22]/V + …………) = P1 + P2 + …..Where P1, P2 ... are the partial pressures of the gases, and this is Dalton's law (the sum of the partial pressures of all the gases occupying a given volume is equal to the total pressure).
P = P1 + P2 +……
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