A Levels Chemistry (9701)•9701/12/O/N/19
Explanation
Standard Enthalpy of Atomisation Defined Steps:
- Define standard enthalpy of atomisation as the enthalpy change for forming 1 mole of gaseous atoms from the element's standard state at 298 K and 1 atm.
- Identify the element as sodium (Na), with standard state as solid metal, Na(s).
- Examine each equation for conversion of Na(s) to Na(g) without additional changes.
- Select the equation matching Na(s) → Na(g).
Why B is correct:
- It represents Na(s) → Na(g), the exact process for ΔH°_at of sodium per the definition of atomisation enthalpy.
Why the others are wrong:
- A: Describes atomisation of iodine (I₂), not sodium.
- C: Shows first ionisation energy of gaseous sodium.
- D: Involves liquid sodium and electron removal, not standard atomisation.
Final answer: B
Topic: Chemical energetics
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