Boiling is the process of rapidly converting a liquid to its gaseous (vapor) state, typically by heating the liquid to a temperature called its boiling point. The boiling of a substance is known as a phase change or phase transition. Chemically, the substance remains the same, but its physical state (or "phase") changes.
The boiling point of a substance is the temperature at which it can change its state from liquid to gas throughout the bulk of the liquid at a given pressure. It should be noted that the boiling point of a substance is sensitive to the pressure of the surroundings. Thus, for example, the boiling point of water is lower at a high altitude than it is at sea level, because the air pressure at high altitudes is lower than that at sea level. Based on this understanding, the boiling point of a substance can be defined as the temperature at which the vapor pressure of the liquid substance is equal to the pressure of the surrounding gases.
