Heat of solution involves two steps that is accompanied by heat change. The energies involved in this steps are

Analysis of the Question

The question asks for the two specific energy processes that occur when a solid ionic solute dissolves in a solvent (usually water) to form a solution.

Explanation of the Concept

When an ionic solid (like sodium chloride) dissolves in water, the process happens in two distinct energetic stages:

1. Lattice Energy ($\Delta H_{lattice}$): This is the energy required to break the strong electrostatic forces holding the ions together in the solid crystal lattice. This process is endothermic (energy is absorbed) because you are breaking bonds.
2. Hydration Energy ($\Delta H_{hyd}$): This is the energy released when the separated gaseous ions are surrounded by water molecules (solvated). This process is exothermic (energy is released) because new attractive forces are formed between the ions and the water molecules.

The overall Heat of Solution ($\Delta H_{soln}$) is the sum of these two:

Step-by-Step Solution

• Step 1: Identify the energy needed to break the crystal lattice. This is the Lattice Energy.
• Step 2: Identify the energy released when the ions interact with the solvent. This is the Hydration Energy.
• Step 3: Compare these with the provided options. Option A correctly identifies these two specific terms.

Conclusion

The heat of solution is essentially the balance between the energy taken in to break the crystal structure and the energy given out when the ions are hydrated.

Exam Tip

Think of dissolving a solid like a "break-up and make-up" process:

• Breaking the lattice (The "break-up") requires energy (Endothermic).
• Hydrating the ions (The "make-up" with water molecules) releases energy (Exothermic). Always remember: Lattice Energy is for the solid, Hydration Energy is for the ions in water!