Page 55 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

Equilibrium I 39
pV=nRT =+ p= (nRT)/V, where n = amount of gas (expressed in
moles)

since concentration [X = (nx/ Vx) is expressed as the number of moles
per cubic decimetre.

+ K,, = K,(RT)*"
where Aug = change in the coefficients of gaseous reagents
I
i.e. ug (gaseous products) - ug (gaseous reactants).
This is a very important relationship, which relates Kp to K,. Do not,
however, mix up the order; this can be remembered by PC-'political
correctness' (not the other way around!).
Note: While the units of & are always derived from the equations as
stated previously, e.g.:

i.e. M~/(MM) =+ no units;

i.e. M2/(MM3) =+ units of M-2;

Kp is always dimensionless, as all pressures are divided by the standard
pressure, e.g. in the latter reaction:

i.e. (bar/bar)2/(bar/bar)1 (bar/bar)3 =$ dimensionless!

Since the partial pressures of gases are normally expressed in bars,
R = 0.08314 dm3 bar K-' mol-I should always be used in Kp