Heat capacity ratios calculated from the Benedict-Webb-Rubin equation state

The ratio of the isobaric heat capacity to the constant volume heat capacity has been calculated over a range of temperatures and pressures for the following hydrocarbons: methane, ethylene, ethane, propane, and n-butane. Graphs and tables of calculated data are presented showing the effect of temperature and pressure on the ratio of the heat capacities for these compounds. The deviations of the heat capacities from ideal gas behavior were calculated by previous investigators from an equation based on the Benedict-Webb-Rubin equation of state, Experimental data were used to evaluate the heat capacities of the ideal gases, and were used together with the calculated deviations to obtain the heat capacities of the non-ideal gas states. The results indicate that the ratio of the heat capacities varies significantly with large changes in pressure at a constant temperature, Calculations which do not allow for this effect may be in considerable error. The calculated ratios of the heat capacities have been compared with the available experimental data, with the gereralized correlation of Edmister, and with calculations based on the Beattie-Bridgeman equation of state