Elements

[Wilson 2E]

Why do substances like O2 have a 0 standard enthalpy of formation?

[Daniel Chen 2L]

I'm not really sure I can explain this all that well, but it's something along the line of this:
You're trying to form the standard state of something from something, yes? So the energy from that is the standard enthalpy of formation. For a substance like O2 gas, which is the standard state of its element, the standard enthalpy of formation for changing O2 gas into its standard state, which is O2 gas, is like trying to change something into what it already is, so you aren't really changing anything. That's why it's 0.

[nehashetty_2G]

When we talk about oxygen or nitrogen gas, we always assume it is in its diatomic form. This is because it the diatomic form the standard state. Therefore, I think of it as being like the standard or 0 kJ/mol because the element is just naturally just found in that state.

[Altamash Mahsud 1I]

Substances like O2 and other diatomic molecules, as well as all other elements found in their natural state have an enthalpy of formation of zero because that is how they are found in nature, so there is no amount of heat (enthalpy) needed to form these compounds, because they are already found like that in nature.

[Omar Selim 1D]

Diatomic molecules such as H2, O2, N2, F2, I2, CL2, and Br2 all have an enthalpy of formation of 0 because it is their naturally occuring state. There is no enthalpy of formation for the way something is already formed. However, if you were to change the molecule, then there would be an enthalpy of formation

[Juliet Stephenson 4E]

Since O₂ and other diatomics are so stable, they tend to form in nature. As a result, there is no enthalpy of formation, as oxygen will already be in this form.

[Naneeta Desar 1K]

It is because since molecules such as O2 and N2 are readily discovered in this state the enthalpy of formation is 0 kJ/mol.

[Veronica Lu 2H]

diatomic elements are steady and are found to be that way in nature so the enthalpy of formation is 0kj/mol

[Noe BM 1J]

Does this means that if I have H2 and want to form H2O, then there would be an enthalpy of formation?

Diatomic molecules such as H2, O2, N2, F2, I2, CL2, and Br2 all have an enthalpy of formation of 0 because it is their naturally occuring state. There is no enthalpy of formation for the way something is already formed. However, if you were to change the molecule, then there would be an enthalpy of formation