# How do you find the bond enthalpy from an equation?

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?

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