The standard enthalpy of formation for which of the element is not zero at 1 bar pressure and specified temperature?

Question

If the enthalpy of sublimation of Li is \(155\,\text{kJ mol}^{-1}\), enthalpy of dissociation of \( \mathrm{F_2} \) is \(150\,\text{kJ mol}^{-1}\), ionization enthalpy of Li is \(520\,\text{kJ mol}^{-1}\), electron gain enthalpy of F is \(-313\,\text{kJ mol}^{-1}\), and standard enthalpy of formation of LiF is \(-594\,\text{kJ mol}^{-1}\), then the magnitude of lattice enthalpy of LiF is ____________ kJ mol\(^{-1}\) (Nearest integer).

Answer 1

Step 1: Standard Enthalpy of Formation Definition. The standard enthalpy of formation for an element in its most stable form at 1 bar and a given temperature is defined as zero. This implies that elements in their standard states possess a standard enthalpy of formation of zero.

Step 2: Option Analysis.

(1) S (Monoclinic): Monoclinic sulfur is the most stable allotrope at 1 bar, hence its enthalpy of formation is zero.
(2) P (White): White phosphorus is not the most stable allotrope under standard conditions, resulting in a nonzero enthalpy of formation.
(3) Br\(_2\) (liquid): Bromine, as a liquid at 1 bar and standard temperature, is in its most stable form, so its enthalpy of formation is zero.
(4) O\(_2\) (g): Oxygen gas is the most stable form of oxygen under standard conditions, and its enthalpy of formation is zero.

Final Answer:

\[\boxed{\text{(4) } O_2 \, (\text{g})}\]

The standard enthalpy of formation for which of the element is not zero at 1 bar pressure and specified temperature?

Show Hint

The Correct Option is D

Solution and Explanation

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