Page 18 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:35 9in x 6in b985-ch01 Elementary Physical Chemistry

State of Matter. Properties of Gases 3

Other (non-SI) units frequently used are:

• Pressure: mmHg or Torr (1 Torr = 133.3Pa) or atm (1 atm =
5
760 mmHg) or 101.325kPa bar (1 bar = 10 Pa)
• Energy: electron volt, eV (1 eV = 1.602 × 10 −19 J)

Equation of state is an algebraic relation between pressure, volume,
temperature and quantity of substance.

1.4. Ideal or Perfect Gas Law

PV = nRT
This Law comprises three different Laws that preceded it.

1) Holding constant n and T gives PV = const or

P 1 V 1 = P 2V 2 Boyle’s Law (1.1)
2) Holding constant P and n gives V/T = const or

V 1 /T 1 = V 2 /T 2 Charles’ Law (1.2)

3) Holding constant P and T gives V/n = const or

V 1 /n 1 = V 2 /n 2 Avogadro’s Law (1.3)

1.5. Evaluation of the Gas Constant, R
The gas constant can be expressed in various units, all having the dimension
of energy per degree per mol.

a) R is most easily calculated from the fact that the hypothetical volume
of an ideal gas is 22.414L at STP (273.1 K and 1 atm). Accordingly,

−1
R = (1 atm)(22.414 L mol )/(273.16 K)
=0.08206 atmL K −1 mol −1 (1.4)

3
b) If V is in cm ,
3
R = (1 atm)(22, 414 cm mol −1 )/(273.16 K)
3
=82.06 atmcm K −1 mol −1 (1.5)