Enthalpy of Atomization: Energy to Form Gaseous Atoms from Standard State

Steps:

• Define enthalpy of atomization as the enthalpy change to convert one mole of an element in its standard state to gaseous atoms at 298 K and 1 atm.
• Identify iodine's standard state as solid I₂(s), not gas.
• Construct the equation for one mole of I(g): start with ½I₂(s) to produce I(g).
• Compare to options: only C matches this balanced equation for one mole.

Why C is correct:

• It represents the standard enthalpy of atomization ΔH_at°, forming 1 mol I(g) from ½ mol I₂(s) per the IUPAC definition for elemental standard states.

Why the others are wrong:

• A: Uses gaseous I₂, ignoring solid standard state.
• B: Uses gaseous I₂ and produces 2 mol I(g), not 1 mol.
• D: Uses correct solid state but produces 2 mol I(g), twice the defined amount.

Final answer: C