Page 69 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

The characteristic equation is usually written

PV = RT (2.13)

3
or for m kg, occupying V m ,
PV = mRT (2.14)

Another form of the characteristic equation can be derived using the kilogram-mole as a

unit. The kilogram-mole is defined as a quantity of a gas equivalent to m kg of the gas,
(e.g. since the molecular weight of oxygen is 32, then 1 kg mole of oxygen is equivalent

to 32 kg of oxygen).

From the definition of the kilogram-mole, for m kg of a gas we have,
m = nM, (2.15)

M is the molecular weight of the gas

n is the number of moles

PV

PV = nMRT or MR = (2.16)
nT

Ro=universal gas constant, and is given the symbol

PV
i.e. MR = R = or PV = T (2.17)
nR
o
nT o

or since MR = Ro then,

R
R = o (2.18)
M

o
Experiment has shown that the volume of 1 mole of any perfect gas at 1 bar and 1 C is
3
approximately 22.71 m . Therefore from equation 2.16
PV 1 x 10 5 x 22.71
R = = = 8314.4 J/mole K
0
nT 1 x 273.15

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