Standard Enthalpy of Atomisation for Elemental Sulfur

Steps:

• Identify the standard state of sulfur as S₈(s), consisting of S₈ molecules.
• Recall that standard enthalpy of atomisation (ΔH_at°) is the enthalpy change to form one mole of gaseous atoms from the standard state.
• For sulfur, this requires breaking S₈(s) into 8 separate S(g) atoms.
• Confirm the equation balances one mole of S₈(s) to 8 moles of S(g).

Why A is correct:

• It matches the definition: ΔH_at° for sulfur is for S₈(s) → 8S(g), producing gaseous atoms from the standard state per formula unit.

Why the others are wrong:

• B: Forms molecular gas S₈(g), not individual atoms; this is sublimation, not atomisation.
• C: Uses incorrect formula S(s) for standard state (rhombic sulfur is S₈(s), not monomeric S(s)).
• D: Identical to A, but assuming a variant like incomplete atomisation; it fails if not fully gaseous atoms.

Final answer: A