Laws of phase transformation in a series of normal paraffins

Abstract

The crystal lattice energy of n-paraffins ( n-C nH 2 n+2 ) is represented as U = ε · n + Δ where ε. n is the energy of molecular side-packing and Δ is the end-group packing energy independent of n. By analyzing molecular packing of n-paramn crystalline modifications R, T and M R it was found that Δ T < Δ M R < Δ R but ε T > ε R , A qualitative interpretation of polymorphism and melting laws in the n-paraffin series is based on these relations. The calculations of the crystal lattice energy at 0°K and free enthalpy at 200°K given for the C 9 to C 10 n-paraffins are in full accord with the previous conclusions and, as a matter of fact, substantiate thermodynamically, by way of n-paraffins, the molecular close packing principle in organic crystals.