Which equation represents the $\ce{N-H}$ bond enthalpy in $\ce{NH3}?$

$$ \begin{align} &\textbf{A.} &\ce{NH3(g) &-> N(g) + 3 H(g)}\\ &\textbf{B.} &\ce{1/3 NH3(g) &-> 1/3 N2(g) + H(g)}\\ &\textbf{C.} &\ce{NH3(g) &-> 1/2 N2(g) + 3/2 H(g)}\\ &\textbf{D.} &\ce{NH3(g) &-> .NH2(g) + .H(g)} \end{align} $$

From what I've learnt, I understand that the bond enthalpy is defined as the energy required to break one mole of a specific bond.

In the question above, I opted for answer C as it was the only one with the products in the form of $\ce{N2}$ and $\ce{H2}.$ But since there are three $\ce{N-H}$ bonds in $\ce{NH3},$ I am unsure about answer B.

Can you clarify this?

  • $\begingroup$ you missed $H_2$ in option c. $\endgroup$ – Tapi Dec 30 '19 at 20:08

Option D is the only one corresponding to the definition "energy required to break one mole of a specific bond" and nothing more.

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  • $\begingroup$ Do you mind explaining what the dots infant of NH2 and H represent? $\endgroup$ – Chris28 Dec 30 '19 at 14:54
  • 1
    $\begingroup$ The dots represent the fact that the species are free radicals (they have unpaired electrons). Strictly speaking, they could have put a dot in front of H in all 4 options and N in option 1. $\endgroup$ – atbm Dec 31 '19 at 7:39

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