Which of the following compounds has a positive enthalpy of solution?

Options

A. LiF
B. LiCl
C. LiBr
D. LiI

Explanation

To determine which of the given compounds has a positive enthalpy of solution, we need to understand the concept of enthalpy of solution and how it relates to the lattice energy and hydration energy of the compounds.

### Step-by-Step Solution:

1. **Understanding Enthalpy of Solution**:
- The enthalpy of solution (\( \Delta H_{sol} \)) is the heat change that occurs when a solute dissolves in a solvent. It can be either positive (endothermic) or negative (exothermic).
- A positive enthalpy of solution indicates that the process absorbs heat from the surroundings, meaning it is endothermic.

2. **Factors Affecting Enthalpy of Solution**:
- The enthalpy of solution is influenced by two main factors:
- **Lattice Energy**: The energy required to break the ionic bonds in a solid lattice.
- **Hydration Energy**: The energy released when ions are surrounded by water molecules.

3. **Analyzing the Given Compounds**:
- The compounds provided are:
- Option 1: LiF (Lithium fluoride)
- Option 2: LiCl (Lithium chloride)
- Option 3: LiBr (Lithium bromide)
- Option 4: LiI (Lithium iodide)

4. **Comparing Lattice Energies**:
- Among these compounds, LiF has the highest lattice energy due to the small size and high charge density of the fluoride ion compared to the other halides.
- Higher lattice energy means that more energy is required to break the lattice structure.

5. **Hydration Energy Consideration**:
- While hydration energy is also significant, in the case of LiF, the energy released during hydration is not sufficient to overcome the high lattice energy required to break the ionic bonds.
- As a result, the overall enthalpy of solution for LiF becomes positive.

6. **Conclusion**:
- Since LiF has a positive enthalpy of solution due to its high lattice energy that is not compensated by hydration energy, the correct answer is:
- **Option 1: LiF (Lithium fluoride)**.