## Thermal Properties of Matter- Class 11 | Chapter – 11 | Physics Short Notes Series PDF for NEET & JEE

Thermal Properties of Matter: Thermal properties of matter refer to the characteristics of a material that relate to its ability to conduct, transfer, and store heat energy. These properties are important in many fields, including physics, chemistry, and engineering.

## Thermal Properties of Matter

Some of the most important thermal properties of matter include:

• Specific heat capacity: The amount of heat energy required to raise the temperature of one unit of mass of a substance by one degree Celsius.
• Thermal conductivity: The ability of a material to conduct heat energy.
• Thermal expansion: The tendency of a material to expand or contract in response to changes in temperature.
• Melting and boiling points: The temperatures at which a material changes from a solid to a liquid, and from a liquid to a gas, respectively.
• Heat of fusion and vaporization: The amount of heat energy required to change a material from a solid to a liquid, and from a liquid to a gas, respectively.
• Specific heat of fusion and vaporization: The amount of heat energy required to change one unit of mass of a material from a solid to a liquid, and from a liquid to a gas, respectively.

## Components of Thermal Properties of Matter

• Thermal expansion
• Thermal stress
• Thermal conductivity
• Heat capacity

Thermal expansion

Thermal expansion is the tendency of matter to expand or contract in response to changes in temperature. When a material is heated, the individual particles that make up the material vibrate faster and occupy more space, causing the material to expand. Conversely, when a material is cooled, the particles vibrate slower and occupy less space, causing the material to contract.

The amount of expansion or contraction depends on the material’s coefficient of thermal expansion, which is a measure of how much a material will expand or contract per unit of temperature change. Different materials have different coefficients of thermal expansion, and some materials expand or contract more than others.

Thermal expansion can have important practical implications. For example, bridges and other large structures made of metal may expand and contract significantly in response to changes in temperature, causing them to buckle or deform if not properly designed to accommodate this expansion. Similarly, glass and ceramics can crack or shatter if exposed to sudden temperature changes due to thermal expansion.

However, thermal expansion can also be useful in certain applications. For example, bimetallic strips, which are made of two different metals with different coefficients of thermal expansion, can be used to convert temperature changes into mechanical motion, such as in thermostats and temperature-controlled switches. Thermal expansion can also be used to secure objects, such as nuts and bolts, by using materials with different coefficients of thermal expansion to create a tight fit when the temperature changes.

Thermal stress

Thermal stress is the stress or strain that occurs in a material when it is exposed to changes in temperature. When a material is heated or cooled, it expands or contracts, and this expansion or contraction can create internal stresses within the material.

Thermal stress can cause a variety of problems, such as warping, cracking, and deformation of the material. For example, when a metal is heated, its coefficient of thermal expansion causes it to expand, and if the expansion is not uniform, it can cause the metal to warp or deform. Similarly, when a material is cooled rapidly, the outer layers contract faster than the inner layers, leading to stress and possible cracking.

The magnitude of thermal stress depends on the thermal expansion coefficient of the material, the temperature change, and the shape and size of the object. Therefore, it is important to consider these factors when designing materials and structures that will be exposed to temperature changes.

To reduce thermal stress, materials with low coefficients of thermal expansion can be used, or materials with different coefficients of thermal expansion can be combined to minimize the overall stress. Additionally, cooling and heating processes can be controlled to ensure that the temperature changes are uniform and gradual, rather than sudden and drastic.

Thermal conductivity

Thermal conductivity is the ability of a material to conduct or transfer heat energy. It is a measure of how easily heat can be transferred through a material, and is usually expressed in units of watts per meter per Kelvin (W/mK).

Materials with high thermal conductivity can transfer heat quickly and efficiently, while materials with low thermal conductivity transfer heat more slowly. For example, metals such as copper and aluminum have high thermal conductivity, while materials such as wood and insulation have low thermal conductivity.

Thermal conductivity is an important property in many applications, such as designing and manufacturing heat exchangers, selecting materials for electronics cooling, and optimizing energy efficiency in buildings. Materials with high thermal conductivity are often used in heat sinks, which are used to dissipate heat away from electronic components. Conversely, materials with low thermal conductivity, such as insulation, are used to reduce heat transfer and improve energy efficiency in buildings.

The thermal conductivity of some of the materials are listed below:

 Materials Thermal Conductivity Metals Silver 406 Copper 385 Mercury 8.3 Non-Metals Insulating brick 0.15 Glass 0.8 Water 0.8 Gases Air 0.024 Argon 0.016 Hydrogen 0.14

Heat capacity

Heat capacity is the amount of heat energy required to raise the temperature of a material by a certain amount. It is a measure of a material’s ability to store thermal energy.

The heat capacity of a material depends on its mass, its specific heat capacity, and the temperature range over which it is being heated. The specific heat capacity of a material is a measure of the amount of heat energy required to raise the temperature of a unit mass of the material by one degree Celsius (or one Kelvin). It is usually expressed in units of joules per kilogram per Kelvin (J/kgK).

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