Why does a gas spread out to fill an entire container when a divider is removed, rather than staying clumped on one side?

Answer

Disordered states vastly outnumber the ordered ones available in the configuration space.

The molecules explore all available microstates, and since the number of ways to be distributed randomly throughout the volume far exceeds the ways to remain segregated in one half, the scattered state is overwhelmingly probable.

Why does a gas spread out to fill an entire container when a divider is removed, rather than staying clumped on one side?
ThermodynamicsLawsystementropy