Thermodynamic study of a phase transition between the ordered and disordered phases and orientational disorder in crystalline <i>p</i>-chloronitrobenzene

Abstract

Heat capacities of the disordered and ordered crystalline phases of p-chloronitorobenzene were measured by adiabatic calorimetry between 6 and 303 K. The disordered phase stable at room temperature shows a glass transition around 245 K, which arises from the freezing of molecular reorientation as evidenced from the magnitude of the residual entropy. The ordered phase that is stable below 279 K was obtained through annealing the disordered phase around 260 K for a long time. The thermodynamic quantities concerning the first-order phase transition between the ordered and disordered phases were determined as Ttrs=279.0 K, ΔtrsH=(4468±5) J mol−1 and ΔtrsS=(16.01±0.05) J K−1 mol−1. Standard thermodynamic functions are tabulated.