HCN thermodynamics

The JANAF value of the enthalpy of formation for HCN was used in the Sandia database and for GRI-Mech 2.11 and the base mechanism in the GRI-Mech 3.0 optimization. It is the average of differing calorimetric measurements and is assigned a large error bar of +/- 2.0 kcal/mole. Therefore the HCN enthalpy was chosen as an optimization variable for those targets to which it is sensitive.

The following values of H(298) for HCN have been reported:

32.3 JANAF tables (1985)

31.1 TRC tables (1991)

30.5 Morley et al (1992)

31.0 Martin (1996)

30.8 Clifford et al (1998)

GRI-Mech 3.0 adopts a value of 31.3 kcal/mole for H(298), near the more recent consensus for this number and at the low end of the polynomial range afforded in the optimization. This value was fixed in the optimization. It corresponds to the enthalpy reported by Horiuchi et al (1951), one of the two differing values cited by JANAF.

References:

Chase, M.W.Jr., Davies, C.A., Downey, J.R.Jr., Frurip, D.J., McDonald, R.A., and Syverud, A.N., JANAF Thermochemical Tables, 3rd ed., J.Phys.Chem.Ref.Data 14, Supp. 1 (1985).

Clifford, E.P., Wenthold, P.G., Lineberger, W.C., Petersson, G.A., Broadus, K.M., Kass, S.R., Kato, S., DePuy, C.H., Bierbaum, V.M., and Ellison, G.B., J.Phys.Chem. 102, 7100 (1998).

Horiuchi, J., Yano, T., and Kanai, K. Shokubai 7, 8 (1951).

Marsh, K.N., Wilhoit, R.C., Gannon, B.E., Baxter, C.A., Das, A., Ferguson, A.M., Gadalla, N.M., Rodgers, A.S., and Somayajulu, G.R., TRC Thermodynamic Tables, Suppl. 65, Texas A&M University Thermodynamics Research Center (1991).

Martin, J.M.L., Chem.Phys.Lett. 259, 679 (1996).

Morley, G.P., Lambert, I.R., Ashfold, M.R., Rosser, K.N., and Western, C.H., J.Chem.Phys. 97, 3157 (1992).