Ammonium chloride (NH₄Cl) doesn't "break up" with water evaporation in the sense that it doesn't chemically decompose. Here's what happens:

1. Dissolving in Water: When ammonium chloride is dissolved in water, it dissociates into its ions:

```

NH₄Cl (s) -> NH₄⁺ (aq) + Cl⁻ (aq)

```

The ammonium ions (NH₄⁺) and chloride ions (Cl⁻) become surrounded by water molecules, forming hydrated ions.

2. Water Evaporation: As water evaporates, the concentration of water molecules decreases. This disrupts the balance between the hydrated ions and the surrounding water.

3. Crystallization: To maintain equilibrium, some of the ammonium and chloride ions recombine and form solid ammonium chloride crystals.

Essentially, the evaporation of water removes the solvent that was keeping the ammonium chloride ions separated. This forces them back together, leading to the formation of solid ammonium chloride.

It's important to note:

* Ammonium chloride is a soluble salt, meaning it readily dissolves in water.

* The process described above is reversible. If you add more water to the solid ammonium chloride, it will dissolve again.

Let me know if you have any other questions.