Short Answer

The boiling point is the temperature at which a liquid changes into a gas rapidly throughout the entire liquid. At this temperature, bubbles of vapor form inside the liquid and rise to the surface. Each pure liquid has a fixed boiling point, such as water, which boils at 100°C at normal atmospheric pressure.

The boiling point remains constant during the boiling process until the entire liquid becomes vapor. It is an important physical property used to identify substances, compare liquids, and understand their behavior when heated.

Detailed Explanation :

Boiling Point

The boiling point is the specific temperature at which a liquid turns into a gas through the process of boiling. At this temperature, the vapor pressure of the liquid becomes equal to the atmospheric pressure around it. This allows vapor bubbles to form throughout the liquid, not just at the surface. These bubbles rise and burst, releasing the gas into the air. The boiling point varies from one substance to another depending on the strength of the intermolecular forces within the liquid.

The boiling point plays a significant role in cooking, scientific experiments, industries, and natural processes. It helps us understand how heat affects liquids and how different liquids behave differently when heated.

How Boiling Point Works

1. Heating the Liquid

As heat is supplied to a liquid:

• Particles absorb energy
• They move faster
• They collide more intensely
• The temperature gradually rises

Eventually, the particles gain enough energy to escape from the liquid.

2. Reaching the Boiling Point

At a certain temperature, the liquid reaches its boiling point. At this stage:

• The vapor pressure inside the liquid equals the external atmospheric pressure
• Gas bubbles form inside the liquid, not just on the surface
• These bubbles rise and release vapor

Once boiling begins, the temperature does not increase further until boiling is complete.

3. Constant Temperature During Boiling

Although heat continues to be supplied, the temperature remains constant at the boiling point. This is because the heat energy is used for:

• Breaking intermolecular forces
• Converting liquid particles into gas

This hidden energy is called the latent heat of vaporization. Only after the liquid has fully turned into gas will the temperature of the gas begin to rise.

Factors Affecting Boiling Point

1. Atmospheric Pressure

Boiling point depends strongly on pressure.

• Higher pressure → higher boiling point
• Lower pressure → lower boiling point

Examples:

• At high altitudes, water boils below 100°C because air pressure is low.
• In a pressure cooker, water boils above 100°C due to high pressure, which cooks food faster.

2. Nature of the Liquid

Different liquids have different boiling points because of the strength of intermolecular forces.

• Strong forces → high boiling point
• Weak forces → low boiling point

Examples:

• Water boils at 100°C
• Alcohol boils at about 78°C
• Liquid nitrogen boils at −196°C

3. Purity of the Liquid

Impurities affect boiling points.

• Impurities generally increase the boiling point
• Example: Adding salt to water slightly raises its boiling point

This is known as boiling point elevation.

Examples of Boiling Points

• Water: 100°C
• Ethanol: 78°C
• Acetone: 56°C
• Liquid oxygen: −183°C
• Liquid nitrogen: −196°C

These values show how widely boiling points vary among different substances.

Importance of Boiling Point

1. Identifying Liquids

Each pure liquid has a unique boiling point, helping in identification.

2. Checking Purity

A pure liquid boils sharply at a fixed temperature, while impure liquids boil over a range.

3. Cooking and Food Preparation

Boiling helps in cooking food, sterilizing water, and preparing beverages like tea and soups.

4. Industrial Applications

Boiling is used in distillation, purification, chemical production, and oil refineries.

Difference Between Boiling and Evaporation

• Boiling: Happens at a fixed temperature throughout the liquid
• Evaporation: Happens at any temperature only at the surface

Boiling is fast, while evaporation is slow.

Conclusion

The boiling point is the temperature at which a liquid changes rapidly into a gas throughout its entire volume. At this temperature, vapor bubbles form and rise to the surface. The boiling point remains constant during boiling and depends on pressure, purity, and the nature of the liquid. It is an essential physical property widely used in science, industry, and everyday life.