The molecules in any material exhibit vibrational motion even at the lowest temperature. The average kinetic energy of these particles results in temperature. That is, the temperature is the result of molecular motion in a substance. Temperature is measured in Celsius, Fahrenheit, Kelvin, etc. On the other hand, heat is the transfer of thermal energy between molecules. What is the hotness or coldness is the temperature and the energy that flows as a difference in temperature is heat. It is measured in Joules. Both are not the same. 

Thermometers are used to measure the temperature of materials. When heat is provided to a liquid, it expands; this is the principle behind its working. The common thermometer is made up of liquid mercury in a glass tube. When it is made in contact with a hot substance, the liquid inside the tube expands, and this expansion is proportional to its temperature. It is calibrated in standard references like the freezing point and melting point of water. We need to record the measurements systematically and uniformly, so a particular scale opts for the purpose. There are temperature scales like Celsius, Fahrenheit. We could convert these temperature scales from one to another.  For example, The conversion from Celsius to Fahrenheit is as follows. It could be converted vice-versa. 

F= (\( \frac{9}{5} \) )* C + 32

Where F: temperature in Fahrenheit scale

            C: temperature in Celsius scale

Ideal gas in low density obeys various laws like Boyle's law, Charles law, etc. These could be merged to form the ideal gas equation. It is 

PV= nRT

Where P: Pressure, V: volume, N: number of moles, R: Gas constant, and T: temperature of an ideal gas.

And at the usual zero degrees Celsius, the real gases follow a linear trend but do not obey perfectly like an ideal gas. The perfect zero condition for it has to be found from extrapolating its temperature curve. Absolute temperature is the temperature when the internal energy of the system becomes zero. That is, there is no movement of particles. Absolute zero temperature is -273.15 degrees Celsius. 

When heat is provided to matter, it expands. For solids, when heat is provided if the expansion is as opposed to volume change. It is called linear expansion. Similarly, if the expansion is in two dimensions it is Area expansion and the change in three dimensions is called Volume Expansion. 

The measure of the change in the dimensions of a body to the temperature is expressed using the Coefficient of expansions. 

Coefficient of Linear expansion \( \alpha \) _L = \( \frac{1}{L}(\frac{\Delta L}{\Delta T} ) \)

Where,\( \Delta L \): change in length

We could measure the change in temperature of a body when an amount of Heat energy is absorbed or released. The amount of heat required to raise the temperature of a unit mass of a substance by unit degree Celsius is termed as Specific Heat Capacity.  If measured in moles, it is Molar Specific Heat.

\( S= \frac{\Delta Q}{\Delta T} \) 

S: Specific heat capacity of the substance

\( \Delta \)Q: Change in heat energy

\( \Delta \)T:Change in temperature

These expressions are required for solving problems.

Calorimetry is the measurement of changes in properties related to heat transfer. The equipment for the purpose is a calorimeter. When a hot body is placed in contact with a colder one, heat flows from the hot body to the cold one. In an isolated system, the amount of heat lost by the hot body will be equal to the heat absorbed by the low-temperature body. Calorimeter obeys this concept. It has a metallic vessel with metal stirrers kept inside an isolated chamber made of wood, ensuring there is no transfer of energy with the environment. This has an opening to insert a mercury thermometer and could be used based on the principle of transfer of energy. The measurement of heat is called Calorimetry.

On giving heat, phase changes occur. When a solid receives heat, its temperature increases to a point where it starts to boil and becomes liquid. This process is called melting or fusion. The temperature at which this happens is called the melting point. If this entire process happens under standard pressure, it is called the normal melting point. When the liquid is heated, it becomes vapor at a particular temperature called the boiling point. This boiling under constant pressure is termed a normal boiling point. If a solid like camphor is heated, it becomes gas through sublimation. The respective temperature and pressure curves are called the fusion, vaporization, and sublimation curves. The intersecting point of all these three curves shows the coexistence of all phases is called the triple point. The process where ice melts under pressure and refreezes when the pressure is reduced is termed relegation.

During the phase transition of ice to water, if we measure the temperature, it would remain constant throughout. Ice at zero degrees Celsius would become ice at 100 degrees and melt, and the temperature remains constant throughout this changing phase. The substance still receives heat or releases heat. This energy is called Latent Heat. There is the latent heat of fusion, Vaporization, etc. 

\( L= \frac{Q}{m} \)

Where L: Latent heat 

           Q: Amount of heat received or released

           M: Mass of the substance

 

Heat transfers from one material to another in various ways. When there is a temperature difference between two substances, due to the collision among neighboring particles, heat transmits. This is called conduction. When a metal rod is heated, the heat moves towards the holding end because of conduction. Conduction is through direct contact and particles don't move from their positions. Convection is the heat transmission due to the movement of fluid (gas/ liquid). Warm air expands and becomes less dense and flows upwards. Land breeze and sea breeze and trade winds are examples of convection. 

Radiation is the transfer of energy without a medium. The heat energy from the sun reaches us through radiation.

Any hot substance will eventually cool down and attain the temperature of its surroundings. Its temperature curve with time would be a decreasing one. The heat is released as radiation. 

Newton had explained that the rate of loss of heat of a hot body is proportional to the temperature difference between the source and the surroundings. It also depends on factors like Area of exposure and nature of the material. This could be written as

\( -\frac{dQ}{dt} = k (T_{2}-T_{1} ) \)

Where T2- T1: Temperature difference

K: constant of proportionality 

And the differential part is the rate of change of heat with time. It could be solved, and the final expression shows that the temperature curve is decreasing exponentially.

 

1. What are the important topics in NCERT class 11 thermal properties of matter? 

• The Ideal gas equation: Pv= nRT
• Newton's law of cooling: The difference in temperature between a source and the surroundings determines the loss of heat from the body. The loss of heat from the source is directly proportional to this difference in temperatures.
• Specific Heat Capacity: The amount of heat required to raise the temperature of one unit of substance by one degree Celsius Is specific heat capacity.  
• Heat Expansion: When heat is provided to a solid substance, a small change in dimension occurs. It is a material property which determines the extent up to which material would change in presence of heat.
• Heat Conduction: Heat transfers from one point to another in various ways. In materials with temperature differences due to the vibration of molecules, heat transmits it is called conduction. If the transfer is made via fluids it is convection and the transmission which doesn’t need a medium is radiation.

2. What is meant by thermal expansion?

When heat is supplied to any state of matter. It expands, if the expansion is in a line it is linear expansion. The expansion is in an area, then it is area expansion and volume is volume expansivity. These are tiny variations that could be expressed using the coefficients of expansion. These vary for different materials depending on their nature.  

3. Its thermal properties of matter, an important chapter for NEET?

It is an essential chapter for the students who are preparing for NEET as well as IIT JEE.  This chapter is the basics of thermodynamics, which is an important subject for Physics and Chemistry and Engineering Graduates. So, a good hold on the foundation would help the student eventually.  

4. What is the thermal property of matter?

When a matter is exposed to heat, it exhibits certain properties. These are called the thermal properties of matter. Important among them are heat capacity, Thermal expansivity, Conductivity, and Thermal Stress. 

5. Does this site contain Thermal Properties Of Matter Ncert Solutions? 

Yes, on this website you could find answers to all the questions in the text in a very detailed manner. Also, this helps to guide the student to attempt and practice more questions in the scope of this chapter. Practicing problems is the key to scoring well in competitive examinations. Step-to-step solutions are available here so that the student could follow these contents very effectively.