Why Boiling Point Of Water Is high: Why, What, How and Detailed Facts


We know that the boiling point of water is 1000C and consists of two hydrogen atoms bonded with a single oxygen atom. But, do you all know why boiling point of water is high compared to ammonia, H2S, alcohols, CH4, HF, etc.?

The oxygen atom is highly electronegative and upon forming bonds with hydrogen atoms it forms two lone pairs. These lone pairs allow the water molecule to form weak interaction with other water molecules thus more energy is required to break these bonds as the O-H bond forms strong intermolecular bonding.

Why is the Boiling Point of Water Lower at High Altitudes?

As per the ideal gas equation PV=nRT, that is temperature is directly related to the pressure on the system.

At higher altitudes the pressure that is felt on the volume of water is low and corresponding to the pressure, the temperature required to boil the water is also reduced and hence the boiling point of water is lower at high altitudes.

According to Charles Law, [latex]V\propto T[/latex] at constant pressure and based on Boyles Law [latex]P\propto \frac{1}{V}[/latex] at a constant temperature.

By rearranging we can write,

[latex]V\propto \frac{1}{P}[/latex]

Combining both the equations we can write

[latex]V\propto \frac{T}{P}[/latex]

The volume of a gas will be proportional to the number of molecules comprising the entire volume, that is, [latex]V\propto n[/latex].

Hence, the equation now becomes

[latex]V\propto \frac{nT}{P}[/latex]

Now, we can write the ideal gas equation as

[latex]PV\propto nT[/latex] 

[latex]PV=nRT[/latex] 

Where R is a gas constant ([latex]R=8.314 \ J/mol.K[/latex])

n is quantity of gas in terms of moles

At lower altitudes, the pressure felt on the object is high because of the heavy overlying atmospheric volume. As we move higher and higher altitude the same is reduced. Since the temperature is directly proportional to the pressure felt on the unit volume of the matter, with reducing pressure, the temperature will reduce in corresponding. Hence, the water boils at low temperatures at higher altitudes.

Why Does Water Have a Higher Boiling Point than Expected?

The heat energy supplied to the matter is necessary to break the covalent bonds between the atoms.

The water molecule is made up of hydrogen and oxygen atom. Since hydrogen has only one valence electron, it is a highly reactive element and forms a strong covalent bond and an enormous amount of energy is required to break this bond.

The water molecule has two lone pairs and forms a weak molecular interaction bond with surrounding water molecules.

why boiling point of water is high
Chemical bonding of water

As a result, more amount of heat is required to be supplied to the water so that it starts boiling. Thus, the boiling temperature of the water goes slightly high than the expected boiling temperature of the water.

Why is Boiling Point of Water High as Compared to Organic Compounds of Similar Molecular Weights?

The boiling point of any substance is defined based on the temperature it requires to change its phase.

In the case of water, the oxygen is bonded with two hydrogen atoms whereas the organic compounds are made up of carbon molecules which has half filled stable electronic configuration, hence less energy is required to break this bond compared to the bonds between water molecules.

The water molecules are formed by the addition of two molecules of hydrogen bonded with one single oxygen atom, while in the case of the organic substances the hydrogen molecules are bonded with the carbon which has only four valence electrons and is considered a half filled stable shell. Hence, less heat energy is required to break the bond between hydrogen and carbon as carbon would easily give away the hydrogen atom to become the most stable atom.

What is the Reason for Unusual High Boiling Point of Water?

The water requires more amount of heat to start boiling and change its state from liquid to vapour.

This is simply because the bonds between hydrogen and oxygen are way stronger as hydrogen is highly reactive and oxygen has two vacant spaces in the valence shell to be filled which it receives by forming strong intermolecular bonds with hydrogen atoms.

Why Boiling Point of Water is Higher Than Alcohol?

The boiling point of a liquid is mainly based on the number of hydrogen bonds present.

The alcohols are made up of hydroxide bond pairing with the carbon atom, that is the oxygen atoms form a pair with only one hydrogen atom while that of a water molecule, two hydrogen atoms are sharing a bond with one oxygen atom.

Apropos to alcohol, the heat energy is required to break only one hydrogen bond while in regards to water molecules two hydrogen bonds need to be supplied with the kinetic energy which is double that required in the case of alcohol.

Why Boiling Point of Water is Higher Than Ammonia?

We know that the water boils at 100 degree Celsius and the boiling point of ammonia is -330 C.

The water molecules form two lone pairs along with the hydrogen bonding, whereas ammonia forms three hydrogen bonds and only one lone pair thus less energy is required to break the bonds in ammonia.

The water molecules consist of two hydrogen atoms bonded with a single oxygen atom and has two lone pair thus making it a stable configuration. On contrary, ammonia is made up of a nitrogen atom making three hydrogen bonds and has only one lone pair. Thus forming only one intermolecular bond in ammonia molecule, whereas, in that of water there are two intermolecular bonds hence more energy is required to break the bonds in water as compared to ammonia molecule.

Why Boiling Point of Water is Higher Than Ethanol?

The boiling point of ethanol is 78.370 Celcius and the molecular formula is C2H6O.

The ethanol has –OH bonding and is in the category of the alcohols. The energy require to break the bonds between the carbon and a single bond between the hydrogen and oxygen is less compared to the energy required to break the strong intermolecular bonds of two hydrogen with one oxygen atom.

As discussed above, we can understand why alcohols require less heat energy to break the bonds as compared to water molecules. Ethanol is also one among the alcohols and has a total of 6 hydrogen bonding but not as strong and stable configuration and the intermolecular bonding as that seen in regards to water.

Why Boiling Point of Water is Higher Than Hydrogen Sulphide?

Both, water as well as hydrogen sulphide forms an equal number of hydrogen bonding but only the atomic number differs.

The bonding between the water molecules is stronger as compared to the hydrogen sulphide because the oxygen atom is smaller than the sulphur. As the sulphur atom is bigger in size the electrons will be hindering from the nuclei of the atom and hence forms a weak force of attraction.

Though the valence electrons of both oxygen and sulphur atom are the same, the atomic number of oxygen is 8 and that of sulphur atom is 16, hence sulphur atom has a bigger atomic radius than the oxygen atom. This difference in the atomic radius makes the intermolecular force of attraction stronger in the atoms with a small radius which is oxygen than the sulphur atom.

Why Boiling Point of Water is Higher than Hydrogen Fluoride?

The boiling point of hydrogen fluoride is 19.500 Celsius which is very less compared to water.

Fluoride is a halogen and can easily react with matter accepting an electron from another to complete its outer shell, on the other hand, the hydrogen atoms react with oxygen forming two bonds thus water molecules become highly electronegative.

More energy is required to break the two bonds in water than the single bond between the hydrogen and the fluoride molecules and therefore the boiling point of water is higher than the hydrogen fluoride.

Why Boiling Point of Water is Higher than Methane?

The chemical formula of methane is CH4 and its boiling point is -1640 Celsius.

The carbon atom forms weak intermolecular bonding between the hydrogen bonds as it has a stable half filled valence shell while the oxygen is highly electronegative than carbon and the O-H bond is stronger than the C-H bond.

The force of attraction between hydrogen and oxygen is far greater than the carbon and hydrogen atoms. Thus more energy is required to break the O-H bond as compared to the C-H bond this is why water has more boiling point than methane.

Frequently Asked Questions

Why boiling point of water is more than HCl?

The boiling point of HCl is -85.050 Celsius which is very less compared to the boiling point of water.

Hydrochloric acid has only one hydrogen bond with chlorine while in the case of water it has two hydrogen bonds with the oxygen atom. Moreover, the atomic radius of the Chlorine atom is more than the oxygen atom thus the force of attraction is low.

Why boiling point of water is more than acetone?

The boiling point of acetone is 560 Celsius at room temperature.

The chemical formula of acetone is C36O and the oxygen forms double bonds with the carbon atom. It has high vapour pressure as compared to water thus the boiling point of acetone is less than water.

Does adding salt to water increase the boiling point of water?

Upon mixing salt with water, the salt will absorb the heat energy supplied to the water.

The amount of heat energy will be utilized to break the bonding between the salt molecules to mix well in the water thus the boiling temperature of the water will slightly go above but remains in approximation to 1000 Celsius only.

How does the boiling point of water affect adding sugar to it?

As the sugar is dissolved in water, the density of the water rises.

Hence, more amount of heat energy is required to boil the water and the boiling point goes up to 2120 Celsius. Once the solution reaches this temperature the water starts evaporating leaving behind the sugar as it is denser.

Click to read more on Boiling Point Under Vacuum.

AKSHITA MAPARI

Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn - linkedin.com/in/akshita-mapari-b38a68122

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