= Bond-dissociation enthalpy
{title2=$\Delta_{\rm diss}H^{\circ}(T)$}
A <bond-dissociation enthalpy> is the molar <enthalpy> change for the specified <homolysis> at <temperature> $T$, with reactant and products in specified <standard states>. Its usual units are $\mathrm{kJ\,mol^{-1}}$. The superscript $\circ$ specifies <standard states>; it does not fix $T$ to room <temperature>.<IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry/bond-dissociation enthalpy>[definition and symbols: standard molar enthalpy for homolysis, Δdiss H°]{ref}
Write $\delta h_i(T)=H_{m,i}^{\circ}(T)-H_{m,i}^{\circ}(0)$ for each species' molar thermal <enthalpy> increment. With $D_0$ an <energy> per parent <molecule>,
$$
\Delta_{\rm diss}H^{\circ}(T)=N_{\rm A}D_0+\delta h_A(T)+\delta h_B(T)-\delta h_{AB}(T).
$$
Here $N_{\rm A}$ is the <Avogadro constant>. The thermal increments include translational <kinetic energy>, <molecular rotation>, thermally excited <molecular vibration> and electronic states when populated, and the $pV$ contribution to <enthalpy>. They are additional to the <zero-point energies> already included in $D_0$. If values of <standard enthalpy of formation> at the same $T$ are available, <Hess's law> gives the same quantity as $\Delta_fH^{\circ}(A)+\Delta_fH^{\circ}(B)-\Delta_fH^{\circ}(AB)$.
Units alone do not identify the convention. Multiplying either $D_e$ or $D_0$ by the <Avogadro constant> gives molar <energy>, but does not add thermal <enthalpy>. One <electronvolt> per dissociation corresponds to $96.485332\,\mathrm{kJ\,mol^{-1}}$. A <spectroscopic wavenumber> $\widetilde\nu$ represents <energy> $hc\widetilde\nu$, using the <Planck constant> $h$ and <speed of light> $c$; $1\,\mathrm{cm^{-1}}$ corresponds to $0.011962657\,\mathrm{kJ\,mol^{-1}}$.<Fundamental Physical Constants — Complete Listing by National Institute of Standards and Technology and others>[SI defining constants h, c, e and Avogadro constant; conversions calculated from them]{ref}
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