Thermophysical Properties of Gaseous HBr and BCl3 from Speed-of-Sound Measurements

The speed of sound in gaseous hydrogen bromide (HBr) and boron trichloride (BCl3) was measured using a highly precise acoustic resonance technique. The HBr speed-of-sound measurements span the temperature range 230 to 440 K and the pressure range from 0.05 to 1.5 MPa. The BCl3 speed-of-sound measurements span the temperature range 290 to 460 K and the pressure range from 0.05 MPa to 0.40 MPa. The pressure range in each fluid was limited to 800 of the sample vapor pressure at each temperature. The speed-of-sound data have a relative standard uncertainty of 0.010. The data were analyzed to obtain the ideal-gas heat capacities as a function of temperature with a relative standard uncertainty of 0.10. The heat capacities agree with those calculated from spectroscopic data within their combined uncertainties. The speeds of sound were fitted with the virial equation of state to obtain the temperature- dependent density virial coefficients. Two virial coefficient models were employed, one based on the hard-core square-well iIntermolecular potential model and the second based on the hard-core Lennard Jones iIntermolecular potential model. The resulting virial equations of state reproduced the speed-of- sound measurements to 0.010 and can be expected to calculate vapor densities with a relative standard uncertainty of 0.10. Transport properties calculated from the hard-core Lennard Jones potential model should have a relative standard uncertainty of 100 or less.