Question

The energy required to completely separate one mole of a solid ionic compound into its gaseous constituent ions is called:

• A. Lattice energy
• B. Ionization energy
• C. Electron gain enthalpy
• D. Sublimation energy

Hint:

Lattice energy is associated with ionic compounds and measures the strength of ionic bonding. Greater lattice energy implies greater stability of the ionic crystal.

Answer 1

The Correct Option is A

Concept: Ionic compounds are made up of positively charged cations and negatively charged anions held together by strong electrostatic forces of attraction. The strength of attraction between these oppositely charged ions is measured in terms of lattice energy. Lattice energy is one of the most important thermodynamic quantities associated with ionic solids. It gives an idea about the stability of an ionic crystal and the strength of ionic bonding present in the compound.

Step 1: Understanding the definition of lattice energy. Consider an ionic solid such as sodium chloride, NaCl. In the solid state, sodium ions and chloride ions are arranged in a three-dimensional crystal lattice. To completely separate this crystal into gaseous ions, \[ \text{NaCl(s)} \rightarrow \text{Na}^{+}(g)+\text{Cl}^{-}(g) \] energy must be supplied to overcome all the electrostatic attractions present in the crystal. The energy required for this process is called lattice energy.

Step 2: Examining the other options. Ionization energy: Ionization energy is the energy required to remove an electron from an isolated gaseous atom. Example: \[ \text{Na}(g)\rightarrow \text{Na}^{+}(g)+e^{-} \] Therefore, ionization energy is not the correct answer. Electron gain enthalpy: Electron gain enthalpy refers to the enthalpy change when an electron is added to an isolated gaseous atom. Example: \[ \text{Cl}(g)+e^{-}\rightarrow \text{Cl}^{-}(g) \] Hence, it is not related to separation of ionic crystals. Sublimation energy: Sublimation energy is the energy required to convert a solid directly into gaseous form without passing through the liquid state. Example: \[ \text{I}_2(s)\rightarrow \text{I}_2(g) \] Therefore, it is different from lattice energy.

Step 3: Conclusion. The energy required to completely separate one mole of a solid ionic compound into its gaseous constituent ions is known as lattice energy. \[ \boxed{\text{Lattice Energy}} \] Hence, the correct answer is \[ \boxed{(A)} \]