In chemistry, boiling point refers to the temperature at which a substance changes from its liquid state to its gaseous state, under normal atmospheric pressure or at a specified pressure. It is the temperature at which the vapor pressure of a liquid becomes equal to the surrounding atmospheric pressure, allowing bubbles of vapor to form within the liquid and escape into the air as a gas.

Key points about boiling point in chemistry include:

1. Definition: The boiling point is the temperature at which the liquid and vapor phases of a substance are in equilibrium. At this temperature, the vapor pressure of the liquid is equal to the atmospheric pressure or the pressure applied to the system.
2. Vapor Pressure: The boiling point is determined by the vapor pressure of the liquid. As the temperature increases, the kinetic energy of the molecules also increases, leading to an increase in the vapor pressure. When the vapor pressure equals the external pressure, bubbles form and the liquid starts to boil.
3. Normal Boiling Point: The normal boiling point is the boiling point of a substance at standard atmospheric pressure, which is usually taken as 1 atmosphere (atm) or 760 mmHg. It is a characteristic property of a substance and can be used for identification and comparison.
4. Pressure and Boiling Point: The boiling point of a substance is influenced by the external pressure. At higher altitudes where the atmospheric pressure is lower, the boiling point of a substance decreases. Conversely, increasing the pressure above the liquid can elevate the boiling point.
5. Boiling Point Elevation: Boiling point elevation refers to the increase in the boiling point of a solvent when a non-volatile solute is dissolved in it. This phenomenon is governed by the Raoult’s law and can be used to determine the molecular weight or concentration of the solute in a solution.
6. Boiling Point Range: For pure substances, the boiling point occurs over a narrow temperature range. However, for mixtures or compounds with varying compositions, the boiling point may be spread over a range of temperatures due to the presence of different components.
7. Boiling Point Determination: The boiling point of a substance can be determined experimentally using various techniques such as distillation, reflux, or the use of a thermometer immersed in the liquid.

The boiling point is an important physical property of a substance as it provides information about its volatility, intermolecular forces, and phase transitions. It has practical applications in various fields, including chemical synthesis, purification, and the design of industrial processes.