In the less extensive technique of "'equilibrium unfolding "', the fractions of folded and unfolded molecules ( denoted as p _ { N } and p _ { U }, respectively ) are measured as the solution conditions are gradually changed from those favoring the native state to those favoring the unfolded state, e . g ., by adding a guanidinium hydrochloride or urea . ( In "'equilibrium folding "', the reverse process is carried out . ) Given that the fractions must sum to one and their ratio must be given by the Boltzmann factor, we have
