Why is the heat of formation for gaseous oxygen equal to 0?

Question: Why is the heat of formation for gaseous oxygen equal to 0?

Answer:
1. The standard heat of formation of any compound is defined as the enthalpy change for the compound when it is formed from its elements in their standard states.

2. Gaseous oxygen (O_2(g)) is a molecule (not a compound). The standard state for oxygen is as a gas, O_2(g).

3. There is no need to change gaseous oxygen, O_2(g) into its standard state because that is how it exists under standard conditions, therefore its heat of formation is 0.

Find out more at, and see worked examples, at https://www.ausetute.com.au/heatform.html