<Dl> <Dd> Z = z N / N! (\ displaystyle Z = z ^ (N) / N!), </Dd> </Dl> <Dd> Z = z N / N! (\ displaystyle Z = z ^ (N) / N!), </Dd> <P> but the intermolecular potential necessitates two modifications to z . First, because of the finite size of the particles, not all of V is available, but only V − Nb', where (just as in the conventional derivation above) </P> <Dl> <Dd> b ′ = 2 π d 3 / 3 (\ displaystyle b' = 2 \ pi d ^ (3) / 3). </Dd> </Dl>

Relation between van der waals constant and critical constant