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Introduction to Physical Chemistry 7
where p = pressure of the gas (measured in bar); V = volume of the gas
(measured in dm'); n = amount of gas (measured in mol); T =
temperature of the gas (measured in IS); R = Universal Gas Constant
= 0.08314 dm3 bar K-' mol-' (or 8.314 J K-' mol-I). The above
equation can also be modified to take into account changes in tempera-
ture, AT, changes in volume, AV, and changes in the coefficients of
gaseous reagents, Au, respectively, i.e. pV = nRAT, pAV = nRT and
pV = Au,RT. ug represents the coefficients in a chemical equation. For
example, in the reaction N2(g) + 3H2(, 4 2NH3(g),
Aug = C[v(Gaseous products)]-C[u(Gaseous reactants)] = [(2)] - [(l)
+ (3)] = -2.

Molar Volume
1 mole of an ideal gas measured at 25 "C and 1 bar pressure occupies
24.8 dm3 (where 1 dm' = 1000 cm3).

i.e. 1 mole of an ideal gas at 25 "C and 1 bar pressure occupies 24.8
1 dm3.

Example: Calculate the amount of gas in moles in 2000 cm3 at
25 "C and 1 bar pressure.

Solution:
At 25 "C and 1 bar pressure, 1 mole of an ideal gas occupies 24.8 dm3
i.e. 24.8 dm' = 1 mol
1 dm3 = (1/24.8) mol
2000cm' = 2dm3 = (2/24.8) mol = 0.081 mol
Answer: 0.081 mol.

KINETIC THEORY OF GASES
Kinetic energy is the energy a body possesses by virtue of its
motion. The molecules of gases travel at high velocity and hence
have high kinetic energy. The kinetic theory of gases is used to
explain the observed properties of gases, of which Brownian motion
provides good evidence. Brownian motion is the irregular zigzag
movement of very small particles suspended in a liquid or gas. If
tobacco smoke is placed in a small cell, well-illuminated on a
microscope stage, the tiny particles appear to be moving at random,
as shown in Figure 1.2(c). This is due to the smaller invisible