Similarly, if a fraction  of  moles of solute associate to form one mole of an n-mer (dimer, trimer, etc.), then
For the dimerisation of acetic acid in benzene:
: 2 CHCOOH  (CHCOOH)
2 moles of acetic acid associate to form 1 mole of dimer, so that
For association in the absence of dissociation, the van 't Hoff factor is: