In the present article, we are intended to discuss the boiling point and molecular forces and how they influence each other.

As the molecular forces of attraction increase, the vapour pressure tends to decrease, which influences the boiling point of that liquid to increase; this is due to the fact that the heat provided is used to overcome the intermolecular forces and to break the respective bonds present in order to produce distinct molecules of that liquid.

Let us now know what boiling point and molecular forces mean in general.

 Boiling point and molecular forces

 Both the boiling point and molecular forces are physical properties.

The boiling point is nothing but the temperature that has to be reached or achieved by the liquid in order for it to form vapours so that it can get changed into a gaseous state. Molecular forces are the type of forces or interactions that operate in a molecule; the two kinds of molecular forces are intermolecular forces and intramolecular forces.

Several physical properties of the compounds which are helpful in the identification of them are the results of these molecular forces. Both the attractive forces and the repulsive forces constitute these molecular forces.

How do we find boiling points by molecular forces?

The two main factors that affect the boiling point are molecular forces and molecular weight.

It is possible to determine the boiling points of the substances by observing which bonds are present as different bonds require different amounts of energy (heat) required to break them so that the gas phase of the substance is achieved.

 Thus, the molecules constituting the liquid having hydrogen bond, such as water, needs more heat to dissociate and form separate molecules.

 Do intermolecular forces increase with the boiling point?

Both the boiling point and molecular forces are interconnected in the following manner.

As the intermolecular attraction forces increase, the vapour pressure tends to decrease, which influences the boiling point of that liquid to increase; This is due to the fact that the heat provided is used to overcome the intermolecular forces and to break the respective bonds present in order to produce distinct molecules of that liquid.

Now, let us discuss the molecular structure and the boiling point.

 How does molecular structure affect boiling point?

Associating the arrangement of molecules, there are three states of matter, i.e., Solid, liquid and gas.

In solids, we can see the tightly packed arrangement of molecules, whereas, in liquids and gases, the molecules undergo motion freely and possess weak (liquid) or no (gas) intermolecular forces. So, we can conclude that, as the tendency of the molecules to move freely away from each other, they are likely to get transformed from liquid to gas.

 i.e., to undergo boiling. Thus, molecular structure affects the boiling point.

The next part focuses on why molecules fifer by their boiling points.

 Why do molecules have different boiling points?

Different molecules are found to have different values of boiling points.

The boiling point is influenced by its molecular weight and Van der Waals forces or molecular forces. We know that these factors differ from molecule to molecule hence boiling point is also different for different molecules.

In the following section, let us discuss the influence of intermolecular forces on the boiling point.

How do intermolecular forces affect the boiling point of a liquid?

 The boiling point of a liquid is also affected by the strength of intermolecular forces present in it.

We all know that vapour pressure is the deciding factor for the boiling point and this vapour pressure depends on the strength of the intermolecular forces. A liquid that has weak intermolecular forces experiences ease to get evaporated as it tends to have high vapour pressure and low boiling point.

 In contrast, A liquid associated with the strong intermolecular forces will not get evaporated with ease as it would have a high boiling point.

Why do molecular covalent compounds have such low boiling points?

Covalent compounds have low boiling points due to the type of bond formed in them.

A bond that is formed due to the equal sharing of electrons between the atoms is itself a covalent bond. We can see that the covalent bond formation does not involve any ions, which makes the attractive forces very weak. i.e., the so-called covalent compounds are held by comparatively a weak intermolecular force.

Thus a lesser amount of heat is also enough to break this force and separate the molecules apart.

 Which of the molecules has the highest boiling point?

By experimental observation, it is concluded that the alkenes do have higher boiling points due to the below-mentioned reason,

Alkenes have more number of carbons compared to other compounds. Due to this reason, the strength of the intermolecular force is large, which in turn results in the increase of the molecule size and also contributes to the deviation of Van Der Waals forces. These facts are responsible for the higher boiling point of higher alkenes.

Frequently asked questions | FAQS

What are all the factors that affect the boiling point of a liquid other than the intermolecular forces?

 The boiling point is said to be influenced by several parameters majorly,

Pressure: The boiling point of the liquid may get deviated due to variation in pressure. If the atmospheric pressure is found to be less than one atmosphere, then the boiling point of that liquid may reduce below the normal boiling point. Similarly, the boiling point may increase above the normal boiling point when the environmental pressure surrounding the liquid exceeds one atmosphere.

Type of molecule: A liquid may be considered to be made up of a certain type of molecule. These criteria also affect the boiling point as they differ by the range of intermolecular forces.

Why do alkenes are found to have higher boiling point temperatures?

By experimental observation, it is concluded that the alkenes do have higher boiling points due to the below-mentioned reason,

Alkenes have more number of carbons compared to other compounds. Due to this reason, the strength of the intermolecular force is large, which in turn results in the increase of the molecule size and also contributes to the deviation of Van Der Waals forces. These facts are responsible for the higher boiling point of higher alkenes.

What is the need for a boiling point?

There are many applications of boiling point, especially in our everyday life. Some of them are mentioned below,

• In cooking food
• Sterilization of medical equipment such as syringes and band-aids
• To regulate the action and reaction of chemical compounds that are used in daily life.

How our daily lives are influenced by boiling point?

The boiling point is defined as when a liquid transforms into a gaseous form.

The boiling point is supposed to have a huge impact on the world around us since it influences the way of cooking food and also the kind of substances that has to be used in the manufacture of most things.

How does a higher or lower boiling point decide evaporation?

The boiling point is a temperature that has to be achieved in order to transform the liquid into gas.

The lower the boiling point, the substance is more likely to get evaporated, i.e., it may get evaporated even when it is provided by a small amount of heat, and the higher the boiling point, it is more unlikely to form vapours as it requires more heat for the formation of bubbles.

What happens if the boiling point of the water is lower than the actual value?

The higher and lower boiling points may cause some difficulties in our daily activities; one of them is given below,

If the boiling point becomes much lesser than the actual value, then it will be more difficult to cook and shower as it becomes very hot even under the provision of less heat. It will not be possible to dip our hands in water, and it would feel really warm while cooking.

Name some of the factors that influence the boiling point

Many criteria are found to be affecting the boiling point of a liquid. Such as,

• Humidity
• Atmospheric pressure
• Altitude
• Molecular weight
• Van Der Waals force

How is the boiling point gets influenced by the temperature?

At the instance of boiling point, the vapour pressure is the same as that of the atmospheric pressure surrounding the liquid.

We can observe that as we go on increasing the temperature by supplying heat, there is an increase in the vapour pressure of the liquid. Whereas when we aim to increase the external pressure, we end up increasing the boiling point also. In general, 760 torrs (at sea level) is the pressure at which the liquids start to boil.

What is the device required to measure the boiling point?

Basically, there is a requirement of mainly two devices so that there is an accurate way of measuring the boiling point.

The devices that constitute the boiling point apparatus are necessary to know the exact value of the boiling point of a liquid. This apparatus consists of a monometer that helps in the effective determination of the vapour pressure along with a thermometer that shows the value of the temperature of the liquid.

 I.e., one of the devices is used to measure temperature and another one to calculate vapour pressure.

What is done to water so that it boils at a temperature below 100 degrees celsius?

We already know that can vary the boiling point due to changes in environmental pressure.

In order to decrease the temperature value at which the water boils, we need to reduce the external pressure surrounding the liquid or by decreasing the humidity present in the air. The same procedure is incorporated in the principle of the pressure cooker.

It basically increases the pressure due to which the water boils at a lower temperature to save energy.

Name some of the properties of intermolecular forces.

Intermolecular forces are also termed Van Der Waals forces, and a few properties regarding the intermolecular forces are,

• All types of atoms or molecules are said to be possessing intermolecular forces if they are close to each other.
• The strength of these forces influences the physical properties of the material (for example: melting and boiling points)

Differentiate between the intermolecular and intramolecular forces.

 Intermolecular and intramolecular forces differ by the entities between which they exist.

What are the examples of the intramolecular forces?

Mainly chemical bonds are due to the intramolecular forces. Below mentioned are some examples of the intramolecular forces. I.e.,

• Covalent bond
• Ionic bond
• Co-ordinate covalent bond

Why is intermolecular force weaker compared to intramolecular forces?

We already know that the intramolecular forces are stronger in comparison to intermolecular forces; this can be interpreted by an example,

In the case of an HCL molecule, there is a presence of a covalent bond between H and Cl atoms. They acquire octet configuration due to this covalent bond and hence become stable because of which they won’t get separated. in contrast, the bond present in between the same two atoms belonging to the two different molecules is due to a weak electrostatic attraction.

Mention the types of intermolecular forces?

The existence of intermolecular forces is seen only when the molecules are in close proximity.

There occur to be many kinds of intermolecular forces. Namely,

• Dipole-induced dipole forces
• Ion-dipole forces
• Dipole-dipole forces
• London forces

What is the reason for the increase in boiling point and molecular forces?

Both the boiling point and molecular forces are seen to be influencing each other.

Molecular forces can be measured by boiling points. When we boost the polarization of bonds, it will increase molecular forces. By increasing the molecular weight of the substance, it is possible to increase the boiling point.

 Surface area also affects the boiling point, and it increases due to an increase in the surface area as they are related to each other by direct proportionality.

Why there is an increase in the boiling point of noble gases down the group in a periodic table?

As the outermost shells of noble gases are filled, they lack the tendency to form covalent bonds, which makes them monoatomic.

As we go down the group, the electronic cloud size increases as the atomic size increases. Therefore, the atoms down the group associate themselves with strong molecular forces, increasing their boiling points.

Why does Ethan is found to have a boiling point lower than that of hexane?

Even though both Ethan hexane is non-polar compounds, they differ by boiling point. Because

Hexane is capable of developing a stronger molecular force of attraction and hence a higher boiling point than that of Ethan. All this is because of the existence of a larger number of atoms in the case of ethane. We know that, at room temperature, hexane is a liquid, and ethane is gas; this is also due to the strong molecular forces.

Why do the boiling point and molecular forces depend on size?

It is found that both boiling point and molecular forces rely on the size of the molecule; this is because,

The size of the molecule or an atom influences the strength of London forces or molecular forces, i.e., the large the molecules larger is the intermolecular force, and thus the boiling point also gets influenced further.

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