Enthalpy of Formation. Thermodynamic Functions

The enthalpy of formation was experimentally determined from the appearance potentials (AP) of the fragments of N2H2 or N2H4. The values show considerable variation, mainly because of the difficulty of accurately measuring these appearance potentials. 

In the most recent study, the appearance potential measured for H2 via N2H2 + e - H2+N2 + 2 e together with the known ionization energy of H2 gave A H as values of 176.1 2.9 and, more probable, 188.3 3.3 kJ/mol (A Hq 183.3 2.9 or 195.0 3.3). The two A H° values result from two different AP(H2) values obtained by analyzing the photoion yield curve of H2 [1]. 

The following table lists the results of quantum-chemical ab initio calculations on 

CASSCF/CI ([4s3p2d1f/3s2p1d] ANO basis) CASSCF/CI Davidson correction (triple zeta 206.3 212.5 [8]-  

Results of computations on a smaller scale (e.g. SCF level, small basis sets) are given in [14 to 20]. 

3 Enthalpy of Formation. Thermodynamic Functions Enthalpy of Formation A H in kJ/mol 

The most recent experimental values of the enthalpy of formation are compiled in the following table  

In a review of published enthalpies of formation, AfHo=192 1 is recommended [5]. The error limit of 1, which Is considerably lower than the error 6.3 In JANAF tables 

The first values of A H, determined from the kinetics of the decomposition of hydrazine 

Several AfH values were calculated on the basis of ab initio methods [19 to 24]. Semiem-pirlcally calculated AfH values are too low [25 to 28]. 

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