Textbook HW section 4E

[AndresElizarraras 2A]

We are given a list of diatomic molecules and their respective bond enthalpies.

If I'm not mistaken, diatomic molecules have a bond enthalpy of 0 because they're in their most stable form? Why Do molecules such as H2 and O2 thus have a listed bond enthalpy?

Thank you.

[Cindy T 3F]

The standard enthalpy of formation of diatomic molecules in their standard state is zero. This is referring to the formation of a substance from its elements. Enthalpy of formation differs from the bond enthalpy, which is the energy stored in a bond between two atoms. H2 and O2 still have energy stored in their bonds, while their enthalpy of formation is zero.

[Audrey Wong 2G]

The standard enthalpy of formation of molecules is 0 for pure elements in their standard states, such as O2(g) and H2(g), but bond enthalpy is different from standard enthalpy for formation. Standard enthalpy of formation is the enthalpy change associated with the formation of a molecule from its constituent pure elements in their standard states, while bond enthalpy is the amount of energy stored within bonds. Therefore, there is still energy within the O--O and H--H bonds, which is why there is a bond enthalpy value listed for each of these bonds.