Correspondence pubs.acs.org/IECR
Response to “Comments on ‘Heats Capacity, Enthalpy of Formation, and Entropy of Methyl Carbamate’” Zuo-xiang Zeng, Si-long Yu, Wei-lan Xue,* and Xiao-nan Li Institute of Chemical Engineering, East China University of Science and Technology, 200237 Shanghai, People’s Republic of China hank you for the comments1 on “Heats Capacity, Enthalpy of Formation, and Entropy of Methyl Carbamate” very much. We have read it carefully and appreciate your hard work on this topic.2 Compared to the Benson group additivity method, which is an accurate group contribution method developed by Benson, the Gaussian-4 method is also one of the most successful theoretical procedures. Both of them can be used to calculate the values of Δf H°(g,298.15 K) and S°(g,298.15 K) of MC. In fact, the errors of Δf H°(g,298.15 K) and S°(g,298.15 K) for MC between the two methods are not large (6.3% and 2.9%, respectively).1,2 The experimental data will determine which method is better for MC. Based on the above data, the values of Gibbs energy change ΔrGcal ° (433.15 K) for the synthesis reaction of MC estimated by the two methods are −7.47 and 24.59 kJ/mol, respectively. At the same time, the average value of the experimental equilibrium constant Kexp ° (433.15 K) is 7.25, from which the value of ΔrGcal ° (433.15 K) calculated by eq 18 in ref 2 is −7.13 kJ/mol. The data of the parameters estimated by the Benson method and the Gaussian-4 method for MC are listed in Table 1. From this table, it can be seen that the Benson method is
T
could lead to better agreement between the experimental and estimated (eq 9 in ref 2) Gibbs energy.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Marochkin, I. I.; Dorofeeva, O. V. Comments on “Heat Capacity, Enthalpy of Formation, and Entropy of Methyl Carbamate”. Ind. Eng. Chem. Res. 2012, DOI: 10.1021/ie3002793. (2) Zeng, Z.-X.; Li, X.-N.; Xue, W.-L.; Zhang, C.-S.; Bian, S.-C. Heat Capacity, Enthalpy of Formation, and Entropy of Methyl Carbamate. Ind. Eng. Chem. Res. 2010, 49, 5543−5548. (3) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K. Gaussian-4 Theory. J. Chem. Phys. 2007, 126, 084108.
Table 1. Values of Parameters Estimated by Benson and Gaussian-4 Method for MC parameter
Benson method
Gaussian-4 method
Δf H°(g, 298.15 K) (kJ mol−1) S°(g, 298.15 K) (J K−1 mol−1) ΔrGcal ° (433.15) (kJ mol−1) Kcal ° (433.15 K) Kexp ° (433.15 K)
−439.8 324.5 −7.47 7.96
−412 315 19.65 0.0011 7.25
more persuasive. Although the values of Δf H°(g, 298.15 K) and S°(g, 298.15 K) for MC calculated by the two methods are approached, the values of the calculated equilibrium constant (Kcal ° (433.15 K)) are at opposite poles, because of the propagation of error. Both of the methods are rational; however, we believe that one of them must be in preference to another for a given substance. For example, the Benson method may be more suitable for MC. On the other hand, in ref 3 (the D part, “Analysis of problem energies”), we can find that some species (usually nonhydrogens) may have problems with the experimental values. Especially, it said “for some nonhydrogen systems these are probably not accounted for by the higher level correction”,3 so the Gaussian-4 method may not be suitable for some nonhydrogen systems. In conclusion, we do not think the new values of enthalpy and entropy of MC proposed by Marochkin and Dorofeeva © 2012 American Chemical Society
Published: March 29, 2012 5374
dx.doi.org/10.1021/ie300582w | Ind. Eng. Chem. Res. 2012, 51, 5374−5374
