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Gernot Friedrichs, H.Gg. Wagner

Direct Measurements of the Reaction NH₂ + H₂ → NH₃ + H at Temperatures from 1360 to 2130 K

The reaction NH₂ + H₂ → NH₃ + H (11) was investigated behind shock waves in the temperature range from 1360 to 2130 K. Time histories of NH₂ were measured by frequency modulation (FM) spectroscopy. The rate constant was determined to be k₁₁ = 4.5 · 1013 · exp[-61 kJ mol^-1/RT] cm³ mol^-1 s^-1 (Δlog k₁₁ = ±0.15, ΔE_a = ±9 kJ/mol).
According to recent literature values the reverse reaction NH₃ + H → NH₂ + H₂ (-11) can be described by k_-11 = 1.5 · 10⁷ · T^2.0 · exp(-47 kJ mol^-1/RT) cm³ mol^-1 s^-1 for the temperature range of 400 to 2500 K. On the basis of k-11 and by using the enthalpy of formation of Δ_fH^o_{298 Κ}(NH₂) = 190 kJ/mol, which was determined in a previous study [1], via detailed balance the following expression for the forward reaction (11) was obtained for a temperature range of 400 to 2200 K: k₁₁ = 1.5 · 10⁴ · T^2.6 · exp(-25 kJ mol^-1/RT) cm³ mol^-1 s^-1. This expression is in very good agreement with the reported experimental values for k₁₁.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 214, 08/2000
Pages: 1151

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