EXCESS MOLAR ENTHALPIES OF NITROUS-OXIDE-OCTANE IN THE LIQUID AND SUPERCRITICAL REGIONS

The excess molar enthalpies H-m(E) of [xN(2)O + (1-x)C8H18] have been measured in the liquid and supercritical region over the whole concent ration range. Mixtures at 308.15 K and 7.64, 9.48 and 12.27 MPa show m oderately endothermic and exothermic mixing in the octane-rich region and nitrous oxide-rich region, respectively. The exothermic-mixing reg ion is confined to a smaller range of x, as pressure increases, and di sappears completely at 308.15 K and 15.00 MPa. Mixtures at 318.15 K an d 7.64 and 9.48 MPa show very exothermic mixing. The magnitude of the minimum observed at 318.15 K decreases as the pressure increases and m ixtures at 318.15 K and 12.27 and 15.00 MPa exhibit endothermic mixing in the octane-rich region. The temperature and pressure effects on th e H-m(E) values are both large and of opposite sign. These effects are discussed in terms of a liquid-vapour equilibrium and critical consta nts for nitrous oxide-octane. Excess enthalpies for nitrous oxide-octa ne mixtures are also calculated using the Peng-Robinson equation of st ate and the resulting H-m(E) values are compared with experiment.