The speed of sound was measured in gaseous nitrous oxide (N2O) and nitric oxide (NO) using an acoustic resonance technique with a relative standard uncertainty of less than 0.01 %. The measurements span the temperature range 200 K to 460 K at pressures up to the lesser of 1.6 MPa or 80 % of the vapor pressure. The data were analyzed to obtain the constant-pressure ideal-gas heat capacity C as a function of temperature with a relative standard uncertainty of 0.1 %. For N2O, the values of C agree within 0.1 % with those determined from spectroscopic data. For NO, the values of C differ from the spectroscopic results by as much as 1.5 %, which is slightly more than the combined uncertainties. The speed-of-sound data were fitted by virial equations of state to obtain temperature-dependent density virial coefficients. Two virial coefficient models were employed, one based on square-well intermolecular potentials, and the second based on a hard-core Lennard-Jones intermolecular potential. The resulting virial equations reproduced nearly all the sound-speed data to within 0.01 % and may be used to calculate vapor densities with relative standard uncertainties of 0.1 % or less.
Citation: International Journal of Thermophysics
Pub Type: Journals
Equation of state, ideal-gas heat capacity, intermolecular potential, N2O, nitric oxide, nitrous oxide, NO, speed of sound, thermodynamic properties