Here's why:
* Vapor Pressure: This is the pressure exerted by the vapor of a liquid when it's in equilibrium with its liquid phase. Essentially, it's the pressure of the gas molecules escaping from the liquid's surface.
* Atmospheric Pressure: This is the pressure exerted by the weight of the air above us.
Boiling Point: The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. At this point, the liquid's molecules have enough energy to overcome the attractive forces holding them together and transition into the gas phase. Bubbles form within the liquid, rise to the surface, and escape.
In short: When vapor pressure and atmospheric pressure are equal, the liquid is at its boiling point and is actively changing into a gas.
