Evaporation

Real World Example

Imagine you're at a crowded concert, and people at the front start to leave early to beat the traffic. This is similar to how molecules at the surface of a liquid gain enough energy to escape into the air, turning into gas. Just like those concert-goers who have enough motivation to leave the crowd and make their way out, molecules at the surface of a liquid with enough energy break free and evaporate into the atmosphere.