This article provides a thermodynamic analysis of DSC data for acetaminophen polymorphic forms I and II by measurement of
heat capacity. Form I is found to have lower heat capacity and free energy and hence better stability than Form II down to
at least –30C. The transition temperature below which Form II becomes more stable was determined to be less than –120C.
Form I is more stable than Form II as a consequence of its higher entropy, since its crystallographic packing arrangement
is of larger energy.