question archive The enthalpy of formation of oxygen (O?) is zero because oxygen is an element and O? is its most stable form
The enthalpy of formation of oxygen (O?) is zero because oxygen is an element and O? is its most stable form
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The enthalpy of formation of oxygen (O?) is zero because oxygen is an element and O? is its most stable form.
The standard enthalpy of formation of a substance is defined as the when 1 mol of the substance is formed from the most stable form of its elements in their standard states at 1 atm.
All elements in their standard states (for example, oxygen in the form of O?, C in the form of graphite, H?, I?, F?) have a standard enthalpy of formation of zero, because there is no change involved when they are formed from themselves.
Note: Only the most stable form of an element has a zero enthalpy of formation.
Ozone (O?) is a less stable allotropic form of oxygen. Its enthalpy of formation is 142.7 kJ/mol.
Diamond is a less stable allotrope of carbon. Its enthalpy of formation is 1.9 kJ/mol.
