Factors Affecting Boiling Point and Vapour Pressure of Liquid

Boiling Point 

The boiling point is the temperature at which a liquid turns into a gas or the point where the vapor pressure of a liquid equals the atmospheric pressure. For example, Water has the chemical formula H2O and is an inorganic substance. It is a translucent, tasteless, odorless, and almost colorless chemical substance that is the primary ingredient of the hydrosphere of Earth and all known living creatures' fluids. At 1 atm (i.e., 101.325 kPa), the typical boiling point is 99.97 °C (211.9 °F). At a standard pressure of 100 kPa (1 bar), the IUPAC-recommended standardized boiling point of water is 99.61 °C (211.3 °F).

 The factors that affect boiling point include:

Factors:
1. Atmospheric pressure: 

The higher the atmospheric pressure, the higher the boiling point. This is because more pressure is required to keep the liquid in a liquid state at a higher temperature.

2. Intermolecular forces: 

The stronger the intermolecular forces of attraction between the molecules of a substance, the higher the boiling point. The reason is that more energy is required to overcome these forces and break the bonds between the molecules.

3. Molecular weight: 

Generally, the higher the molecular weight of a substance, the higher the boiling point. This is because more energy is required to overcome the stronger intermolecular forces between larger molecules.

4. Presence of impurities: 

The presence of impurities in a substance can lower its boiling point. This is because impurities disrupt the intermolecular forces between the molecules, making it easier to convert the liquid into a gas.

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  Factors Affecting Boiling Point 

Vapour Pressure 

Vapor pressure is defined as the pressure exerted by the vapor of a substance in a closed system when it is in equilibrium with its liquid or solid phase at a particular temperature. In simpler terms, it is the measure of the tendency of molecules in a liquid to escape into the atmosphere as a gas or vapor. As an example, when water vapor molecules are gaseous, they exert pressure on the surrounding environment. Water has a vapor pressure of 23.8 mmHg at 298K. 

Factors:
There are several factors that affect vapor pressure, including:

1. Temperature: 

Vapor pressure increases with an increase in temperature. This is because at higher temperatures, more molecules have sufficient kinetic energy to escape from the liquid and become a vapor.

2. Intermolecular forces: 

The strength of intermolecular forces between molecules affects vapor pressure. Stronger forces lead to lower vapor pressure as molecules are more tightly held in the liquid phase.

3. Molecular weight: 

The higher the molecular weight of a substance, the lower the vapor pressure. This is because heavier molecules have weaker kinetic energy and are less likely to escape the liquid phase.

4. Surface area: 

An increase in surface area leads to an increase in vapor pressure. This is because more molecules are available to escape into the atmosphere, increasing the likelihood of vaporization.

5. Presence of other gases: 

The presence of other gases can affect vapor pressure. If the gas is less dense than air, it will tend to rise and decrease the pressure at the surface of the liquid, leading to an increase in vapor pressure.

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  Factors Affecting Vapor Pressure of Liquid 

Example:

An example of the relationship between boiling point and vapor pressure is the difference between water and acetone. The boiling point of water is 100℃, while the boiling point of acetone is much lower at 56℃. This indicates that acetone has a much higher vapor pressure at room temperature than water.

This is because acetone molecules have weaker intermolecular forces than water molecules, meaning that more of them can escape into the atmosphere at a given temperature. As a result, acetone evaporates more quickly than water and has a higher vapor pressure.

In contrast, water has stronger intermolecular forces and a higher boiling point, which makes it less likely to evaporate at room temperature. This is why water is a liquid at room temperature, while acetone is a volatile liquid that easily evaporates.