Some Physical Properties of Compressed Gases. II, Carbon Monoxide

The writers have adjusted and extrapolated the compressibility data obtained by Bartlett and his collaborators on carbon monoxide, so that accurate p-v-T relations from -70^∘{} to 400^∘{} and up to 1200 atm. are available. The relatively low pressure isotherms of Scott at 25^∘{} and of Goig-Botella at 0^∘{}, 12.44^∘{}, and 20.22^∘{} are included. Derivatives are obtained by the graphical scheme used for similar calculations on nitrogen. The specific volume, density, expansion coefficients --- (p/v)(dv/dp)T and (T/v)(dv/dT)ₚ fugacity, Cₚ, Cₚ-Cᵥ, Cᵥ, Joule-Thomson coefficient μ are calculated and shown in curves and a table for 14 pressures and 11 temperatures in the range -70^∘{} to 400^∘{} and 25 to 1200 atm. In particular, Cₚ vs. p isotherms, Cᵥ vs. t isobars, t vs. pμ=const. graphs are shown; among the last, the μ=0 curve is the inversion curve. There are no direct experimental data for comparison. On account of similarity in the molecular structure and the spectra of the molecules CO and N₂, one might look for some correspondence in the physical properties of the two gases. In general, the trends of the two are qualitatively similar. The Cₚ-Cᵥ vs. p isotherms all show a maximum. This maximum is very flat at the highest temperatures and comes at about 700 atm. As the temperature decreases, the maximum becomes pronounced and moves to lower pressures; it comes at about 200 atm. along the -50^∘{} and -70^∘{} curves. Along the -70^∘{} isotherm a second maximum appears at about 550 atm., but it is not evident at higher temperatures. Cₚ-Cᵥ approaches R, of course, along all isotherms as the pressure is decreased to zero. Cₚ is obtained by adding ΔCₚ to Cₚ*.Cₚ* denotes the heat capacity for a given temperature at zero pressure; ΔCₚ is the change in Cₚ with pressure along a given isotherm. It is evaluated thru ∫0ᵖT(d²vdT²)ₚdp. The derivative occurring under the integral sign is obtained by the authors' graphical scheme at a sufficient number of points for mechanical integration under the isotherm. Along isotherms at 50^∘{} and lower, Cₚ increases rapidly with pressure and reaches a maximum at about 300 atm. Changes in pressure above 500 atm. cause only relatively small changes in Cₚ at any temperature. Above 200 atm. and below 0^∘{}, Cₚ increases rapidly as the temperature is lowered. The Cᵥ vs. t isobars show that from 300 to 1200 atm. Cᵥ has a minimum at about 100^∘{}. On the low temperature side of this minimum the curves are very steep; along the 1200 atm. isobar Cᵥ drops from 4.4 R at -70^∘{} to 2.57 R at 100^∘{}. Above 100^∘{}, Cᵥ is only a few hundredths cal./mole deg. higher than Cᵥ* for pressures up to 400 atm; further increase in pressure to 1200 atm. raises Cᵥ only a few tenths. Below 25^∘{}, Cᵥ for $p=25$ is slightly less than Cᵥ*. Below 0^∘{}, Cᵥ at 100, 150, and 200 atm. drops far below Cᵥ* as the temperature is lowered. A graph showing Δ≡v(pvRT-1) vs. ρ isotherms and isobars is shown, the data for which are listed in the table. This graph is very convenient for interpolating p-v-T data. Having given two of the three p-v-T coordinates, the third is quickly estimated from the graph, or is readily computed more exactly by reading the ordinate Δ and solving Δ=v(pvRT-1) for the unknown desired. Values for the second virial coefficient are found. They are expressible by B=58.03-19.84 T^-1 cc/mole between -70^∘{} and 400^∘{}.