Some Physical Properties of Compressed Gases. II, Carbon Monoxide

Abstract

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 — $\left(\frac{p}{v}\right){\left(\frac{\mathrm{dv}}{\mathrm{dp}}\right)}_T$ and $\left(\frac{T}{v}\right){\left(\frac{\mathrm{dv}}{\mathrm{dT}}\right)}_p$ fugacity, $C_p$, $C_p-C_v$, $C_v$, Joule-Thomson coefficient $\mu$ 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, $C_p$ vs. $p$ isotherms, $C_v$ vs. $t$ isobars, $t$ vs. $p\mu =\mathrm{const}$. graphs are shown; among the last, the $\mu =0\mathrm{}$ 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 ${\mathrm{N}}_2$, 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 $C_p-C_v$ 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. ${\mathrm{C}}_p-C_v$ approaches $R$, of course, along all isotherms as the pressure is decreased to zero. $C_p$ is obtained by adding $\Delta C_p$ to ${C_p}^{*}.{C_p}^{*}$ denotes the heat capacity for a given temperature at zero pressure; $\Delta C_p$ is the change in $C_p$ with pressure along a given isotherm. It is evaluated thru $\int 0^{p}T{\left(\frac{d^{2}v}{d{T}^2}\right)}_p\mathrm{dp}$. 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, $C_p$ increases rapidly with pressure and reaches a maximum at about 300 atm. Changes in pressure above 500 atm. cause only relatively small changes in $C_p$ at any temperature. Above 200 atm. and below 0°, $C_p$ increases rapidly as the temperature is lowered. The $C_v$ vs. $t$ isobars show that from 300 to 1200 atm. $C_v$ has a minimum at about 100°. On the low temperature side of this minimum the curves are very steep; along the 1200 atm. isobar $C_v$ drops from 4.4 $R$ at -70° to 2.57 $R$ at 100°. Above 100°, $C_v$ is only a few hundredths cal./mole deg. higher than ${C_v}^{*}$ for pressures up to 400 atm; further increase in pressure to 1200 atm. raises $C_v$ only a few tenths. Below 25°, $C_v$ for $p=25\mathrm{}$ is slightly less than ${C_v}^{*}$. Below 0°, $C_v$ at 100, 150, and 200 atm. drops far below ${C_v}^{*}$ as the temperature is lowered. A graph showing $\Delta \equiv v\left(\frac{\mathrm{pv}}{RT-1\mathrm{}}\right)$ vs. $\rho$ 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 $\Delta$ and solving $\Delta =v\left(\frac{\mathrm{pv}}{RT-1\mathrm{}}\right)$ for the unknown desired. Values for the second virial coefficient are found. They are expressible by $B=58.03-19.84\mathrm{} T^{-1\mathrm{}}$ cc/mole between -70° and 400°.