Melting and Boiling Point

Melting and Boiling Point of a substance are the temperatures at which the state of matter changes from solid to liquid and liquid to gas respectively. These two temperature points are important to understand the physical properties of matter.

In this article, we will learn about the melting point, boiling point definition, their characteristics, factors affecting them, and boiling and melting point of some commonly known elements.

What is Melting Point?

Melting Point of a substance is the temperature at which matter exists both in the solid and liquid state. At this temperature transition of matter from solid to liquid takes place. When the temperature of the substance is below its melting point then matter exists in the solid state whereas, when the temperature of the substance rises above its melting point then matter changes to the liquid state.

Melting Point Definition

Melting Point is defined as the temperature at which the phase transition of matter from solid to liquid takes place.

Melting Point

Characteristics of Melting Point

Some the characteristics of melting point of a substance are discussed below:

• During transition, i.e., change of state from solid to liquid form, the temperature of the substance remains constant.
• Different materials have different melting point due to presence of different range of intermolecular spaces between molecules.
• Melting of a substance takes place due to absorption of heat.
• Melting of a substance takes place at specific temperature of the substance.

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What is Boiling Point?

Boiling Point of a substance is defined as a temperature at which matter exists both in liquid and gaseous state. At this temperature transition of substance from liquid to solid takes place. When the temperature of the substance is above the boiling point then matter exists in gaseous state, whereas when temperature of the matter is below its boiling point then it exists in liquid state. Boiling point is a temperature at which the vapor pressure is equal to the surrounding pressure.

Boiling Point Definition

Boiling Point is defined as the temperature at which matter changes from liquid to gaseous state.

Boiling Point

Characteristics of Boiling Point

Some the characteristics of boiling point of a substance are discussed below:

• Boiling of a substance is affected by atmospheric pressure, i.e., boiling point of the substance decreases at low pressure and increases at high pressure.
• There is wide range of boiling point of matter.
• Many environmental factors like humidity, altitude may directly or indirectly affect the boiling point of the substance.
• Boiling points of the substance is affected by its physical properties like molecular shape and size.

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Determination of Melting Point

Melting point of a substance is a temperature at which vapor pressure of the substance is equal to the atmospheric pressure. The principle and method of determination of melting point are discussed below.

Principle of Determination of Melting Point

During the process of melting, all the energy is provided to a substance as the heat of fusion and temperature of the substance remains constant. A pure crystalline substance has a sharply defined melting point. Pure substance becomes clear and transparent when it reaches its melting point.

A capillary tube melting point, which is also known as complete melting point is a temperature at which a heated substance becomes a clear liquid and the lower end of the capillary tube.

Method of Determination of Melting Point

The determination of melting point can take place via capillary tube method. In this method a thermometer, capillary tube and the sample to be tested is required. The procedure of the capillary tube method is described below:

Step 1: A small amount of sample substance is grounded in a rotating motor.

Step 2: This homogeneous powered substance is then dried in a desiccator using a drying agent such as Phosphorous Pentaoxide.

Step 3: The capillary tube is then filled with sample substance with height between 2mm to 3mm.

Step 4: Heat the apparatus till it reaches the temperature 5-10°C and then lower the temperature such that the temperature of the apparatus rises about 1°C/minute.

Step 5: When the sampled substance is changed into a clear transparent liquid, note that reading of thermometer.

The noted temperature at which the sample substance became a clear transparent liquid is the melting point of the substance. Thus, there is complete disappearance of solid phase of the substance, and it is changed to complete transparent liquid.

Melting point is thus determined by the capillary tube method as the temperature when the substance has just completely melted.

Examples of Melting and Boiling Point

Some of the commonly known examples of Melting and Boiling Point are mentioned below:

Melting Point and Boiling Point of Water

Melting Point of Water is 0 ℃ and Boiling Point of Water is 100℃.

Melting and Boiling Point of Sodium

Melting Point of Sodium is 97.8℃ and Boiling Point of Sodium is 883℃.

Melting Point and Boiling Point of Oxygen

Melting Point of Oxygen is -218.79℃ and Boiling Point of Oxygen is -183℃.

Melting Point and Boiling Point of Hydrogen

Melting Point of Hydrogen is -259.16℃ and Boiling Point of Hydrogen is -252.87℃.

Melting Point and Boiling Point of Magnesium

Melting Point of Magnesium is 650℃ and Boiling Point of Magnesium is 1090℃.

Melting Point and Boiling Point of Nitrogen

Melting Point of Nitrogen is -210℃ and Boiling Point of Nitrogen is -195.8℃.

Melting and Boiling Points of Various Elements

Melting and boiling point of some common elements are listed in the following table:

Element	Melting Point	Boiling Point
Iron (Fe)	1538°C	2861°C
Lithium (Li)	180.5°C	1342°C
Mercury (Hg)	-38.9°C	356.7°C
Calcium (Ca)	839°C	1484°C
Chlorine (Cl)	-101°C	-34.7°C
Aluminum (Al)	660.3°C	2519°C
Zinc (Zn)	419°C	907°C
Copper (Cu)	1083°C	2595°C
Sulfur (S)	115.21°C	444.6°C
Lead (Pb)	327.5°C	1749°C

Factors Affecting Melting and Boiling Point

There are various factors which affects the melting and boiling point of the substance. Some of them are listed below:

• Nature of Bond: Based on the type of bonding present in a substance, boiling and melting point can be affected. When an ionic bond is present in a compound then it generally has high melting and boiling point due to presence of ions, whereas compounds having covalent bond have relatively low melting and boiling point due to less energy requirement to break covalent bonds.

• Intermolecular forces: When intermolecular forces between molecules is larger than it requires more energy to overcome such large force.

• Molecular nature: Nature of a molecule of the substance also affects the melting and boiling point of the substance. Properties like molecular shape, size and alignment or packaging of molecules in a substance greatly affects its melting and boiling point.

• Impurities: Due to the presence of impurities melting and boiling point of the substance differs from its pure state. Type of impurity determines the temperature at which melting and boiling of the substance occurs.

• Crystal defects: Due to the presence of defects in solids (like Frankel defect, Schottky defect) melting and boiling point of the substance is affected.

Difference between Melting and Boiling Point

Some of the differences between melting and boiling point are discussed below:

Melting Point vs Boiling Point
Melting Point	Boiling Point
During the process of melting matter changes from solid state to liquid state.	During the process of boiling matter changes from liquid state to gaseous state.
It occurs between a specific range of temperature.	It occurs at a particular fixed temperature.
Less heat energy from external source is required to obtain melting point as only has to break bonds which was existing between the molecules.	More heat is required from an external energy source as it has to overcome intermolecular forces between the molecules which exists in liquid state.
It occurs only at the surface of the solid.	It occurs throughout the entire mass of the liquid.
Examples of melting point of some substances are: Lead (Pb): 327.5°C Ice: 0°C Aluminum (Al): 660.3°C	Examples of boiling point of some substances are: Lead (Pb): 1749°C Water: 100°C Aluminum (Al): 2519°C

Similarities between Melting and Boiling point

Apart from many differences, melting and boiling point of the substance share some common characteristics and behavior. Some of them are discussed below:

• Intermolecular spaces between the molecules increases due to absorption of heat energy during melting as well as boiling of the substance.
• During melting and boiling of the substance, phase transition of a matter takes place.
• Density of a matter decreases during melting and boiling of a substance.

Melting Point and Boiling Point – Conclusion

Melting and boiling point of a substance is a characteristic feature of a material and is greatly affected by its physical and chemical properties. Every substance has unique boiling and melting point which makes them suitable for different purposes, like in industries different materials are used in different appliances to perform the required operations from it. In essence, by knowing the melting and boiling point of a substance various properties of a material can easily be determined.

Melting Point and Boiling Point – FAQs

What is meant by Melting and Boiling?

Melting is the conversion of a matter from its solid state to liquid state and boiling is the conversion of matter from liquid state to vapour state

What do you mean by Melting Point of a substance?

Melting point of a substance is the temperature at which matter changes its state from solid to liquid. It occurs in particular range of temperature.

Which Metal has Lowest Melting Point?

Gallium (Ga) has lowest melting point in all metals. It has melting point of (29.76°C) due to the weak bonding between gallium atoms. It melts at room temperature.

What do you mean by Boiling Point of the substance?

Boiling point of the substance is a temperature at which matter changes its state from liquid to gas.

What is Anomalous Expansion of Water?

All substances expand of heating on contract on cooling, but water has a peculiar property. When it is cooled it contracts till it reaches to 4°C. If it is further cooled, then from 4°C it began to expand till it reaches to 0°C. This abnormal expansion of water from 0°C to 4°C is called as anomalous expansion of water.

What is MP and BP of Water?

Water has melting point of 0°C (32°F) and has a boiling point of 100°C (212°F).

What is the difference between Melting and Boiling Point?

Melting point of a substance is the temperature at which matter changes from solid to liquid while Boiling point of a substance is a temperature at which the substance changes its state from liquid to gas.

What is Mixed Melting Point?

Mixed Melting Point is a technique of identifying organic chemical compounds. It states that if two pure substances melt at the same temperature, determining mixed melting point help in identifying if they are one or different substance.