Boiling point is the temperature at which a liquid converts to gas (vapor) at normal atmospheric pressure. This is also called the normal boiling point or standard boiling point. The temperature at which a chemical boils is an important characteristic of that chemical. It is used to determine the physical state of a chemical and it serves as an indicator of volatility for non-chemists. It is often included in Section 9 of Safety Data Sheets.

When a liquid is heated it increases its vapor pressure until it becomes equal to the atmospheric pressure. At that point, the forces of attraction between molecules are no longer sufficient to hold the molecules together. The molecules begin to separate and they rise from the liquid in the form of bubbles. The bubbles contain a gaseous substance and they are called vapor.

A liquid’s boiling point is determined by its chemical properties and the environmental conditions it is in. For example, water has a lower boiling point at higher temperatures and when it is colder. The normal boiling point is also affected by surrounding pressures. The higher the ambient pressure, the lower the boiling point.

Impurities in a liquid also increase the boiling point. For example, dissolving salt or sugar in water raises its boiling point. This is one of the reasons why a blend of gasoline has to be specified with an octane rating. This is because the individual additives will have varying boiling points, and the composition of the overall mixture influences the overall octane rating of the blended fuel.