Ideal Gases

One mole is the quantity of substance whose mass (g) is equal to the substance's molar mass (g/mol).

EX: Carbon 12. Molar mass is 12g/mol and 1 mol has a mass of 12 g.

Avogadro's Constant. Na = 6.02 x 1023 this is the number of molecules or atoms or nuclei that are in ONE mol. This is true for any substance.

1 Liter = 1 dm3 = 0.001 m3.

Pressure = Force/Area. Microscopic understanding of Pressure on page 9 of Thermal Organized Notes.


PV = constant

V/T = constant

P/T = constant


Ideal Gas Law: PV = RnT. R = 8.31 J/(mol K). A gas that obeys this law at all temperatures, pressures, and volumes is said to be an ideal gas. Q7 - Q14. We also know that:

  • PV = constant
  • V/T = constant
  • P/T = constant

Alternative Form: PV = kNT. N = number of molecules or atoms. k = Boltzman constant = 1.38 x 10-23

Energy of an Ideal Gas.

  • All KE (why?)
  • KE = 1.5NkT ... this confirms that KE is directly proportional to temperature.


Ideal gases follow the Ideal Gas Law (they cannot be liquified). Real gases can approximate to ideal behavior providing that the intermolecular forces are small enough to be ignored. For this to apply, the pressure/density of the gas must be low and the temperature must be reasonably high


HW. Page 181: 1-9, 15, 16, 17.

MIT Lecture (6:55 - 30:25)




Pressure conversions


Simulation: Gas Properties

PhET questions for Gas Properties (solutions)