As it should be, this K remains unitless. Now, because P/RT is a constant at
constant temperature, for K to remain constant when the volume (V) of the system
is reduced, the ratio nN2O4 /(nNO2)2 must increase. That is, the amount of NO2 must
decrease and the amount of N2O4 must increase. Therefore, as we have seen before,
as the volume of the system is decreased, the equilibrium shifts to a smaller total
number of gas molecules. Conversely, if the system were expanded, more NO2
would be produced and the equilibrium would shift in the direction of a larger total
number of gas molecules.