* Increased Kinetic Energy: Heating a gas increases the kinetic energy of its molecules. This means the molecules move faster and collide more frequently.

* Expansion: The increased kinetic energy causes the molecules to spread out and occupy a larger volume.

* Reduced Density: Density is defined as mass per unit volume. Since the volume increases while the mass remains the same, the density decreases.

In summary:

* Heating a gas leads to:

* Increased molecular kinetic energy

* Expansion of the gas

* Lower density