Question

What is the standard enthalpy of atomization?

Answer 1

Hint: Enthalpy of atomization, is the change in enthalpy when one mole of bonds is completely broken to obtain atoms in the gas phase or the enthalpy change accompanying the dissociation of all the molecules in one mole of gas phase substance into gaseous atoms. For diatomic molecules, enthalpy of atomization is equal to the enthalpy of bond dissociation.

Complete answer:
The enthalpy of atomization is the enthalpy change that accompanies the total separation of all atoms in a chemical substance. This is often represented by the symbol $\Delta {H_{at}}$. All bonds in the compound are broken in atomization and none are formed, so enthalpies of atomization are always positive. Standard enthalpy of atomization is the enthalpy change when one mole of a substance is dissociated completely into atoms under standard conditions.
The heat of atomization is a positive value always and can never be a negative number. We can calculate the enthalpy of atomization when pressure is held constant, the heat change is equal to the change in the system's internal energy. Hence, the enthalpy of atomization is equal to the sum of the total enthalpies of vaporization and fusion. When a diatomic element is converted to gaseous atoms, only half a mole of molecules will be needed, as the standard enthalpy change is based purely on the production of one mole of gaseous atoms. When the atoms in the molecule are different isotopes of the same element the calculation becomes non-trivial.

Note:
The key difference between enthalpy of atomization and bond dissociation is that enthalpy of atomization describes the energy required to separate a molecule into its atoms whereas the enthalpy of bond dissociation describes the dissociation of chemical bonds in a molecule.