# How do we formulate DeltaH_f^@ for "carbon tetrachloride", and HCl?

Sep 2, 2017

We can quote $\Delta {H}_{f}^{\circ}$, the enthalpy change of formation.....

#### Explanation:

And $\Delta {H}_{f}^{\circ}$ represents the enthalpy associated with formation of one mole of substance from its elements in their standard states under standard conditions, i.e. for ${\text{CCl}}_{4}$:

$C \left(s\right) + 2 C {l}_{2} \left(g\right) \rightarrow {\text{CCl}}_{4} \left(l\right)$

And DeltaH_"rxn"^@-=DeltaH_f^@("CCl"_4)

And likewise......

$\frac{1}{2} {H}_{2} \left(g\right) + \frac{1}{2} C {l}_{2} \left(g\right) \rightarrow H C l \left(g\right)$

And $\Delta {H}_{\text{rxn}}^{\circ} \equiv \Delta {H}_{f}^{\circ} \left(H C l\right)$