# Comparing strength of the C-H, N-H, and O-H bonds

\begin{align} \ce{CH4(g) + Cl(g) &-> CH3(g) + HCl(g)} &\quad ΔH^\circ &= \pu{-14 kJ mol-1}_\mathrm{rxn}\\ \ce{NH4(g) + Cl(g) &-> NH2(g) + HCl(g)} &\quad ΔH^\circ &= \pu{-36 kJ mol-1}_\mathrm{rxn}\\ \ce{H2O(g) + Cl(g) &-> OH(g) + HCl(g)} &\quad ΔH^\circ &= \pu{+40 kJ mol-1}_\mathrm{rxn} \end{align}

41. Based on the data above, what can be concluded regarding the strength of the $$\ce{C-H}$$, $$\ce{N-H}$$, and $$\ce{O-H}$$ bonds in the molecules shown?

(A) The $$\ce{C-H}$$ bond is the strongest.
(B) The $$\ce{N-H}$$ bond is the strongest.
(C) The $$\ce{O-H}$$ bond is the strongest.
(D) Nothing can be concluded without knowing the strength of the $$\ce{H-Cl}$$ bond.

I am not sure how to approach the problem 41. In exothermic reactions, more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants. So would the answer be B because the $$ΔH$$ is exothermic and is the greater than $$ΔH$$ of -14 for A?

• "ΔH is exothermic" – no, it's the process/reaction that is. Also, you are not only supposed to compare the signs of the enthalpies, but also per how many bonds it is provided. – andselisk May 6 '19 at 7:06