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Thermal Properties of Matter

Calorimetry

What does heat do to matter? Ever thought about it? If you had all the ice-cream in the world, how big or powerful refrigerator would you require to keep it frozen? That is what we study in Calorimetry. From ice-creams to the inside of a star, let us see how warm our Universe really is!

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What is Calorimetry?

‘Calorimetry’ is the branch of science which measures the changes in the heat energy of a body. We all know that heat is a form of energy. The amount of heat in a body is indicated by its temperature. Therefore, greater the temperature, more is the heat energy of a body. Hence, to know if a body has gained heat energy or lost it, we measure the temperature of the body before and after the transfer. This difference in temperature determines the change in heat energy of the body.

Calorimetry

Suppose you make a cup of coffee while studying this topic or you grab an ice-cream. Initially, the coffee is hot and steaming and its temperature is about 800C . Now assume you have a friend come over at your place and you begin chatting with him.

In this process, an hour passes and the coffee cools down or the ice-cream melts. But why does this happen? This happens because the coffee loses its heat energy to the surroundings and its temperature drops. In case of the ice-cream, it gains heat from the surroundings and its temperature raises. So the new temperature range lies in the range of 30-40 0C.

So, where did the heat energy initially present in the Coffee cup go? And where did the energy that melts our ice-creams come from?

Obviously, the heat energy of the coffee cup is transferred to the surroundings. The same surroundings are responsible for melting our ice-cream too! This is exactly the premise of the topic of Calorimetry. Mind you, this topic deals only with the transfer and conversion of ‘Heat’ energy into other forms of energy like work and vice versa.

System

The body which is under study, on which work is being done or to which heat is being added or which is doing work, or giving out heat is a ‘System’. A System has a fixed amount of mass and has a definite boundary. For example, in the example above the coffee cup is the ‘ System’ under study.

Boundary

The ‘Boundary’ is a real or an imaginary surface, either movable or stationary which separates a system from the surroundings. In the example discussed above, the surface of the coffee cup serves as a real boundary.

Surroundings

The region around the system outside the boundary is the “surrounding”. For the purpose of the study, we assume the entire universe separated from the system by the boundary as the ‘Surrounding’.

Specific Heat

‘Specific heat’ is a property of a substance like density, boiling point etc. We define it as the amount of heat that we add to raise the temperature of a unit mass of the substance through 1 degree. We measure it in Joules/gm K or Joules per gram degree Kelvin and denote it by the letter C. For eg: The Specific Heat of water is 4.1813 J/gm K.

Change in temperature (ΔT)

The change in temperature is the modulus of the difference between the initial and final temperatures of the system. We denote it by ΔT =   (Tfinal  –  Tinitial)

Total Heat Energy (Q)

‘Q’ is the symbol used to denote the total heat exchanged by the system. We have Q = mCΔT; where m is the mass of the system.

Example 1: What is the amount of heat required to change the mass of 1 g of water by 30 °C. Given that C of water is 4.2 J/gm K.
Solution: Given: m= 1g;C=4.2J/gm K; ΔT=30
We know that heat energy required Q= mCΔT
Therefore Q= 1×4.2×30 = 126 Joules.

Thus we have covered here the basics of Calorimetry. This subject finds a lot of application in modern physics, chemistry and their applications. Therefore, Heat transfer during various Physical and Chemical changes is studied in Calorimetry.

More Solved Examples For You

Example 2: The branch of physics that deals with the measurement of heat energy is known as:

A) Fermentation    B) Latent Heat   C) Calorimetry    D) Hidden Heat

Solution: C) Calorimetry is the branch of Physics that deals with the measurement of heat energy. Calorimetry is one of the methods for the determination of specific heats or latent heats of the substances.

Example 3: On which law is the study of calorimetry based?

A) Joule’s Law    B) Law of Conservation of Energy   C) Law of Kinetic Energy   D) None

Solution: B) The Calorimetric studies are wholly based on the law of conservation of energy. Hence, if energy were not conserved, we would never be able to measure heat with a practical level of certainty.

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