Here's why:

* Dissolution is an endothermic process for KNO3: This means that energy is absorbed from the surroundings when KNO3 dissolves in water.

* Spontaneity is determined by Gibbs Free Energy (ΔG): ΔG = ΔH - TΔS

* ΔH is the enthalpy change (positive for endothermic reactions)

* T is the temperature in Kelvin

* ΔS is the entropy change (generally positive for dissolution)

At low temperatures:

* ΔH (positive) is the dominant factor.

* The negative value of TΔS is smaller than ΔH.

* Therefore, ΔG is positive, and the dissolution is non-spontaneous.

At high temperatures:

* The TΔS term becomes more significant as temperature increases.

* If the temperature is high enough, TΔS can become larger than ΔH.

* ΔG becomes negative, and the dissolution becomes spontaneous.

In summary:

* KNO3 dissolving in water is non-spontaneous at low temperatures because the energy required to break the ionic bonds in KNO3 is greater than the energy gained from the increased entropy.

* At higher temperatures, the entropy gain becomes more significant, and the dissolution becomes spontaneous.

There exists a specific temperature (the solubility temperature) above which KNO3 will spontaneously dissolve in water. This temperature is determined by the balance between enthalpy and entropy changes.