Reference Label Details
Pittam 1972D. A. Pittam and G. Pilcher, J. Chem. Soc. Faraday Trans. I 68, 2224-2229 (1972)
Measurements of Heats of Combustion by Flame Calorimetry. Part 8. Methane, Ethane, Propane, n-Butane and 2-Methylpropane
note CH4aPittam 1972 performed measurements of heats of combustion of lower alkanes, where the amount was determined from the CO2 evolved. The apparatus was calibrated by combustion of H2. For methane the reported combustion enthalpy is -890.71 +- 0.38 kJ/mol at 25.00° C. However, that seems to contain an erroneous correction for non-ideality. Also, the enthalpy of combustion of H2O that was used is slightly lower than either the value used here or that adopted by CODATA Key Vals. Going bact to their data in Table 1 and introducing a slight correction for the calibration produces -890.707 +- 0.430 kJ/mol, where the uncertainty is 2.5706 times std. dev. (0.167 kJ/mol) and represents the 95% confidence limit. The correction for non-ideality is -0.0007 kJ/mol (rather than the apparent -0.02 kJ/mol used by Pittam 1972) if one uses Hideal - Hreal of 8.06 J/mol for O2, 41.4 J/mol for CO2 and 8.06 + 15.9 x + 17.4 X^2 J/mol for (1-x) O2 + x CO2 mixtures, where x is the mole fraction of CO2 from Rossini 1939 and 15.5 J/mol for CH4 from Pittam 1972. The composition corresponds to CH4 + 3.5 O2. With this correction and the correction for molecular weight of CO2 from the 1961 scale (44.00995) to 1999 scale (44.0095) produces -890.699 +- 0.430 kJ/mol for the enthalpy of combustion of CH4 at 25.00° C