I think ders a formula for this :
@ = (D(t) - D(o)) / [(n - 1)D(o) ]
If D(t) and D(o) are the theoretical and observed vapour densities at a definite temperature and @ be the degree of dissociation of a substance. Then, find @ in terms of D(o),D(t) and n (number of moles of products formed from 1 mole reactant).
An→nA
1 0
1-a na
Let the molecular mass of An=M
And at equilibrium, M'
then we have, at equilibrium
(1-a)M+na(M/n)=(1+na-a)M'
M-M'=a(n-1)M'
a=M-M'(n-1)M'
a=D(t)-D(o)(n-1)D(o) VD=M/2