Evaporation

Real World Example

Imagine you're trying to get the last bit of toothpaste from a nearly empty tube. Just like squeezing the tube pushes the remaining toothpaste out, the molecules at the surface of a liquid gain enough energy to escape into the air as gas. In both cases, it's about the transition from a contained state (toothpaste in the tube, liquid molecules) to a more dispersed one (toothpaste on your toothbrush, gas molecules in the air), where a small change in conditions allows the substance to move to a new phase.