# Chapter 11 – Thermal Properties of Matter

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Every matter across the universe has particular properties of its own. Same goes for the matter that forms you. Broadly the properties of matter are physical or chemical. While the chemical properties define the way matter reacts, physical properties such as temperature are measured or perceived without altering the particle’s chemical nature (identity). Here, you will learn about the thermal properties of matter

Suppose you heat a metal rod and a cup of water. As heat passes through them, their temperature changes; this temperature change is due to the respective matter’s thermal properties. Even if the metal rod and a cup of water get hot at the same temperature, their reaction to this external heat is different. A metal rod reddens and expands with external heat, whereas; a cup of water will boil and vaporize. On the application of heat, a material may expand in size, transfer heat from one end to another, resist the heat transfer, or not react at all. The type of reaction shown by the material depends on the respective thermal properties. Thermal properties affect the way a material reacts when the heat is applied. Let us discuss these properties one by one.

1. Heat capacity
2. Thermal expansion
3. Thermal conductivity
4. Thermal stress

#### Heat capacity

Heat capacity or thermal capacity is a quantitative property. It is the amount of heat energy required to raise the temperature of matter by a certain amount. Suppose you want to boil a cup of milk. The milk’s heat capacity is the amount of energy required to raise the temperature by a few degrees. It is a ratio of the required amount of heat energy and the temperature change. Where S= heat capacity of the substance = amount of heat supplied to the substance = change in the temperature observed.

Though the heat capacity is a quantifiable property, you need to understand that measurements are futile if they cannot be compared. Hence, keeping water in retrospect, a new measurement called specific heat capacity was started to use. Specific heat capacity is the amount of heat energy required by any substance to change the unit mass temperature by one unit. In simple words, it is the heat energy required to change the temperature of 1 unit mass of a substance by 1 degree.

The formula for specific heat capacity is Or Where s= specific heat capacity of the substance

S= heat capacity of the substance

m= unit mass of the substance

SI unit for measuring the specific heat capacity is joule per Kelvin per Kilogram or J kg–1K–1. Uniquely, the specific heat of material changes with the change in the phase of the material.

For example, the Specific heat of water at liquid state= 1

Specific heat of water at solid state (ice) = 0.5

Specific heat of water at vapor state = 0.4

#### Thermal expansion

Do you know, blacksmiths and goldsmiths are well aware of something called thermal expansion. Because the weld iron or gold, respectively. Both these metals show different degrees of thermal expansion. Thermal expansion is the property of any material to expand when subjected to heat. Whenever a substance is supplied with heat energy, its size increases; the increase in size can be either linear, area, or volume expansion. In general, substances expand, but exceptions are present.

Linear expansion: The expansion in length is termed linear expansion. For example, when an iron rod is heated, it expands only linearly.

The coefficient of linear expansion is Where α1 = coefficient of linear expansion = change in length of the object after the expansion due to heat

l = length of the object = change in temperature

Area Expansion: The expansion in the area of an object is termed as area expansion. When a sheet of metal is heated, it shows area expansion; that is how thin sheets of metal are made.

Volume expansion: The expansion in the volume of an object is termed as volume expansion. Any material expands. A peculiar example is the expansion of water when heated to 4 degrees celsius.

The coefficient of volume expansion is Where the αv= coefficient of volume expansion

V =ha original volume of the object = change in the volume of the object after the expansion due to heat

#### Thermal conductivity

You might know conduction, convection, and radiation. Let’s study a little more about the formal one. The property of any material to allow heat to pass through it is known as thermal conductivity, such as water, metal rod, etc. Any given material conducts heat through it; the more the thermal conductivity, the higher will be the heat conducted through the material. Lower thermal conductivity will result in less conduction of heat through the material. Materials that don’t conduct thermal conductivity are known as insulators. Thermal conductivity is denoted by K; SI units are Watts per meter-Kelvin (W.m-1K-1).

It is a constant of any given material, and it depends on the rate of heat flow, area of material, length of the material, and temperature change observed H= rate of flow of heat through the material

K = Thermal conductivity of the material

A= Cross-section area of the material

(Tc- Td) = temperature difference during/after the conductivity of heat

L= length of the material

In general, the conductivity of solids is higher in comparison to liquids and gases. The highest thermal conductivity is of metals.

#### Thermal stress

The type of stress experienced by the object due to either thermal expansion or compression is thermal stress. Whenever a material undergoes thermal expansion, the material’s inherent property prevents it from increasing, resulting in thermal stress. For example, the railway tracks exhibit thermal stress and result in deformation. When the thermal stress of any matter is more than the thermal expansion, the potential stress can result in the object’s explosion due to the fracturing or plastic deformation.

#### FAQs

Q1. What is the meaning of thermal properties?

A1. The properties of matter that decide how a material reacts when the heat passes through it or when the temperature changes are known as thermal properties. Heat capacity, thermal expansion, thermal conductance, and thermal stress are thermal properties of matter.

Q2.What are the thermal properties of a polymer?

A2. Thermal properties of a polymer are a polymer’s characteristics that help evaluate the tendency of heating, cooling, expanding or resistivity of a material. It includes heat conductivity, melting transition temperature, glass transition temperature, heat setting, thermal expansion, flammability, etc.

Q3.What are the thermal properties of water?

A3. Thermal properties of water include high latent heat of fusion and high latent heat of vaporization. Water has a strange property of exhibiting maximum density at 4°C compared to 0°C. Water expands above and below 4° C. Boiling point of water is 100° C; the melting point is 0° C.

Q4.What is the SI unit of thermal conductivity?

A4. SI unit of thermal conductivity is Watts per Meter-Kelvin (W.m-1K-1).

Additional characteristics of matter measured include boiling and melting points, molar specific heat at constant pressure, constant temperature, and others. To dwell deep into more interesting concepts such as how the thermal properties influence a material’s reactivity or how different types of materials have different properties? Login to the MSVGo learning website or download the MSVgo application. MSVGo is a leading online learning website that provides formulas and explains concepts so that you acquire knowledge from basics to applications. MSVgo,, is a downloadable application that provides a video library of diverse topics explained in simplistic, detailed, and innovative ways that include animations and diagrams.

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