Gases

Boyle's law :     p V = constant  or p₁ V₁ = p₂ V₂   ( constant T and fixed mass of gas)

Pressure law :      

                            ( constant V and fixed mass of gas )

Charles' law :              

                            ( constant p and fixed mass of gas)

Ideal gas equation : pV = n R T 

   where  n = number of moles

              R = the universal molar gas constant ( = 8.31 J K^-1 mol^-1 )

              T = the temperature of the gas in kelvins.

Saturated and unsaturated vapours

       1.           The s.v.p. increases with temperature.

       2.           The s.v.p. is not affected by volume (at a constant temperature).

       Unsaturated vapour obeys gas laws fairly well. The saturated vapour does

        not obey the gas laws.

Interpretation of Temperature : 

  = the average translational kinetic energy (k.e.) of a molecule.

Van der Waals' equation of state for a mole of a real gas is

( p + a/V² ) ( V -b ) = R T

The first law of Thermodynamics

              ΔQ = ΔU + ΔW   

       where    Δ Q = heat absorbed by the system

                        Δ W = work done by the system

                        Δ U = change of internal energy

Isothermal process ( a constant temperature process ) :

   ΔQ = 0 + ΔW = ΔW.

Adiabatic process (no heat enters or leaves the gas and so ΔQ = 0) :

ΔU = 0 – ΔW = -ΔW

Isobaric process ( a constant pressure process ) :  ΔW = p ( V_f - V_i )

Isovolumetric process ( a constant volume process ) :

ΔW = 0.      ΔQ = ΔU.