Here's why:

* Increased Kinetic Energy: As temperature increases, the molecules of both the solute and solvent gain kinetic energy. This means they move faster and collide more frequently.

* Breaking Intermolecular Forces: The increased kinetic energy helps overcome the intermolecular forces holding the solute particles together, allowing them to break apart and dissolve.

* Enhanced Solvation: Higher temperatures also increase the solvent's ability to solvate (surround) the solute particles, further aiding the dissolving process.

Exceptions:

* Gases: Gases dissolve *less* well at higher temperatures. This is because the increased kinetic energy allows the gas molecules to escape from the solution more easily.

* Liquids: The effect of temperature on liquid solute solubility is less predictable and depends on the specific liquid. Some liquids become more soluble with increasing temperature, while others become less soluble.

In summary:

* Solids: Generally more soluble at higher temperatures.

* Gases: Generally less soluble at higher temperatures.

* Liquids: Variable, depending on the specific liquid.