A chemical reaction which the hydration energy is greater than the lattice energy is referred to as

1. Analyze the question The question asks what kind of process occurs when the hydration energy of an ionic compound is greater than its lattice energy. This is about the energy changes when an ionic solid dissolves in water.

2. Explain the concept When an ionic solid dissolves, two energy changes happen:

• Lattice energy: the energy needed to break the ionic lattice into separate ions. Energy is absorbed here.
• Hydration energy: the energy released when the separated ions are surrounded by water molecules. Energy is released here.

The enthalpy of solution is:

ΔH(solution) = Lattice energy − Hydration energy

(Here lattice energy is taken as the positive energy needed to break the lattice.)

3. Solution

• If hydration energy > lattice energy, more energy is released than absorbed.
• Then ΔH(solution) is negative.
• A negative ΔH means heat is given out to the surroundings, so the process is exothermic.

Checking the other options:

• A. Spontaneous: this depends on Gibbs free energy (ΔG), which includes entropy, not on energy comparison alone.
• B. Endothermic: this would be the case if lattice energy > hydration energy.
• D. Reversible: this describes whether a reaction can go in both directions, which is unrelated to this comparison.

4. Answer

5. Tip Remember: "Hydration Higher → Heat Hurled out" (exothermic). If the lattice energy is higher, the dissolving takes in heat (endothermic) and the solution feels cold, as with NH₄NO₃ dissolving in water.