Boiling Point

What is boiling point

The boiling point is the The temperature at which a substance in the liquid state changes to the gaseous state. This occurs when the vapor pressure of the substance is equal to the pressure outside the substance.

This means that the boiling point depends on the external pressure. When this pressure is equal to 1 atmosphere (atm), the boiling temperature is called the normal boiling point.

boiling point explanation

For example, him boiling point of water at 1 atm is 100 °C. When water is boiled at a pressure of 2 atm the boiling point is 120ºC. This is the principle of pressure cookers, the water “boils” at a higher temperature and therefore the food is cooked in less time.

The boiling point of metals is higher than that of water, while the boiling point of alcohol is lower. Below is a table with the boiling point in centigrade of some substances at atmospheric pressure of 1 atm.

examples of boiling points

Substance Boiling point
Water 100ºC
Acetone 56.5ºC
Hydrochloric acid -85ºC
Ethyl alcohol (ethanol) 78ºC
Isopropyl alcohol (isopropanol) 82.4ºC
Methyl alcohol (methanol) 65ºC
Sodium chloride NaCl 1465ºC
Nitrogen N2 -252ºC
oxygen O2 -183ºC
Mercury 357ºC
Methane -162ºC
Lead 1740ºC
Silver 2212ºC

See also: Boiling and Evaporation.

Difference Between Boiling Point and Melting Point

The boiling point and melting point are the temperatures at which a substance changes from one state to another.

You may be interested:  Optics

In the case of the melting point, it is the transition of a substance from the solid to the liquid state, while the boiling point is the temperature at which a liquid substance changes to the gaseous state.

The boiling point temperature will always be higher than the melting point, that is, the temperature for a liquid substance to evaporate into its gaseous state will be higher than the temperature for the solid substance to become a liquid.

See also Melting point and Changes of state of matter.

References

Murphy, P. (2007) Teaching Structure-Property Relationships: Investigating Molecular structure and Boiling Point. J. Chemical Education, 84:87-101 DOI:10.1021/ed084p97

Atkins, PW (1999) Physical Chemistry, 6th ed. Omega Editions. Barcelona