Why Are Addition Reactions to N2 Thermodynamically Unfavorable?

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• 作者：Weston Thatcher Borden
• 刊名：Journal of Physical Chemistry A
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：1140-1144
• 全文大小：252K
• ISSN：1520-5215

文摘

Thermochemical data are used to show that, of the 89.9 kcal/mol difference between the endothermicity of H₂ addition to N₂ (ΔH = 47.9 kcal/mol) and the exothermicity of H₂ addition to acetylene (ΔH = −42.0 kcal/mol), less than half is due to a stronger π bond in N₂ than in acetylene. The other major contributor to the difference of 89.9 kcal/mol between the enthalpies of hydrogenation of N₂ and acetylene is that the pair of N–H bonds that are created in the addition of H₂ to N₂ are significantly weaker than the pair of C–H bonds that are created in the addition of H₂ to acetylene. The reasons for this large difference between the strengths of the N–H bonds in E-HN═NH and the C–H bonds in H₂C═CH₂ are analyzed and discussed.