When heat is applied to a liquid, the vapor pressure of the liquid increases until it equals that of the atmosphere (the gaseous pressure). The temperature at which the vapor pressure of a liquid is the same as the pressure of the surrounding atmosphere is its boiling point.
Liquids only undergo this process, and the boiling point is always higher than the melting point of the same material, because the molecules are much larger in a liquid than in a gas. This makes it difficult for them to escape from the liquid state.
The boiling point of gases can be determined by comparing the temperature at which pure nitrogen or oxygen becomes a gas to the temperature at which room air liquifies. For example, the boiling point of oxygen is 90.6 degrees C and the boiling point of nitrogen is 77 K.
Generally, the lower the boiling point of a gas, the more flammable it is. For this reason, the boiling point of a gas is an important safety factor in handling or storing it.
In chemistry, the boiling point of a chemical is the temperature at which the vapor pressure of the chemical equals that of 760 torr of atmospheric pressure, or one atmosphere. Boiling points are also useful in determining a chemical’s volatility.
The boiling point of a substance is used to indicate the liquid or gaseous phase of a compound at ambient or room temperature, and it serves as a measure of a substance’s volatility even for laymen. It is also an input to equations that give estimates of a chemical’s vapour pressure.