Short Answer

The melting point is the temperature at which a solid changes into a liquid. At this temperature, the solid absorbs heat, and its particles gain enough energy to break free from their fixed positions. Every pure solid has a specific melting point. For example, ice melts at 0°C.

The melting point remains constant during the entire melting process and does not increase until the whole solid becomes liquid. It is an important physical property used to identify substances and check their purity.

Detailed Explanation :

Melting Point

The melting point is a physical property of matter that tells us the exact temperature at which a solid turns into a liquid. At this specific temperature, the solid absorbs heat, its particles gain energy, and the strong intermolecular forces that hold them in fixed positions begin to weaken. As a result, the solid loses its rigid structure and becomes a liquid. The melting point is different for different substances, depending on how strong the forces of attraction are between their particles.

The melting point of a substance is useful in many fields such as chemistry, medicine, cooking, engineering, and material science. It helps scientists identify substances, test purity, and study the behavior of materials at various temperatures.

Understanding the Melting Point Process

1. Heating the Solid

When a solid is heated, it absorbs heat energy. This heat increases the vibration of its particles. In solids, particles are tightly packed and can only vibrate in place. As heat is added:

• Particle vibration increases
• Kinetic energy rises
• Particles begin to push away from each other

This is the beginning stage of melting.

2. Reaching the Melting Point

At a certain temperature, the solid reaches its melting point. At this stage:

• Particles have enough energy to overcome the strong forces holding them
• The solid starts turning into a liquid
• Both solid and liquid states exist together for some time

The important thing to note is that the temperature remains constant during melting.

3. Constant Temperature During Melting

Even though heat continues to be supplied, the temperature does not rise once the solid reaches its melting point. This is because the extra energy is used for:

• Breaking intermolecular forces
• Changing the structure from solid to liquid

This energy is known as latent heat of fusion. Only after complete melting, the temperature of the liquid begins to rise again.

4. After Melting – Liquid State

Once the entire solid melts:

• Particles are no longer in fixed positions
• They slide past each other
• The liquid flows and takes the shape of the container

The melting point becomes an important reference temperature for identifying and comparing substances.

Factors That Affect Melting Point

1. Strength of Intermolecular Forces

• Strong forces → High melting point
• Weak forces → Low melting point

For example:

• Ionic solids like salt and metal have high melting points
• Wax and butter have low melting points

2. Purity of the Substance

Pure substances have sharp, fixed melting points.
Impure substances melt over a range of temperatures.

Example:
Adding salt to ice lowers its melting point.

3. Pressure

Pressure has a small effect on melting.
Increasing pressure generally increases the melting point, except for water, which behaves differently.

Examples of Melting Points

• Ice: 0°C
• Wax: 60°C – 70°C
• Iron: 1538°C
• Gold: 1064°C
• Butter: around 32°C

These differences show how melting points vary widely among substances.

Importance of Melting Point

1. Identifying Substances

Each pure solid has a unique melting point. Scientists use it to identify unknown materials.

2. Checking Purity

Pure substances melt at a sharp temperature; impurities make melting occur over a range.

3. Industrial Uses

Melting points help decide temperatures for metal casting, cooking, manufacturing, and chemical processes.

4. Natural Processes

Melting of snow, ice caps, butter, and chocolate all depend on melting points.

Conclusion

The melting point is the temperature at which a solid changes into a liquid. At this temperature, particles gain enough energy to break free from their fixed positions. It remains constant during melting and is an important physical property for identifying, testing purity, and understanding materials. The melting point varies from substance to substance and depends on particle attraction, purity, and pressure.