Here's why:

* Molecular Motion: As temperature increases, molecules within a liquid gain more kinetic energy and move around more rapidly. This increased motion disrupts the cohesive forces between molecules, making it easier for them to slide past each other.

* Intermolecular Forces: Viscosity is directly related to the strength of intermolecular forces. Stronger forces (like hydrogen bonding) lead to higher viscosity. Increased temperature weakens these forces, reducing viscosity.

* Fluid Flow: Think of viscosity as resistance to flow. The higher the viscosity, the more difficult it is for a liquid to flow. When molecules move more freely due to higher temperature, the fluid flows more easily, meaning lower viscosity.

Exceptions:

While this is the general trend, there are a few exceptions:

* Water: Water's viscosity actually increases slightly between 0°C and 4°C due to the unique arrangement of its molecules in that temperature range.

* Some polymers: Some polymers exhibit a complex relationship between viscosity and temperature, sometimes increasing with temperature due to their unique molecular structures.

In summary: For most liquids, increasing temperature leads to a decrease in viscosity because of the increased molecular motion and weakening of intermolecular forces. This makes the liquid flow more easily.