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Chapter: 11th Physics : Heat and Thermodynamics

Heat capacity and specific heat capacity - Thermal Properties of Matter

Specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of 1kg of a substance by 1 Kelvin or 1°C

Heat capacity and specific heat capacity

 

Take equal amount of water and oil at temperature 27°C and heat both of them till they reach the temperature 50°C. Note down the time taken by the water and oil to reach the temperature 50°C. Obviously these times are not same. We can see that water takes more time to reach 50°C than oil. It implies that water requires more heat energy to raise its temperature than oil. Now take twice the amount of water at 27°C and heat it up to 50°C , note the time taken for this rise in temperature. The time taken by the water is now twice compared to the previous case.

We can define ‘heat capacity’ as the amount of heat energy required to raise the temperature of the given body from T to T + ∆T .

Heat capacity S = ∆Q / T

Specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of 1kg of a substance by 1 Kelvin or 1°C


Where s is known as specific heat capacity of a substance and its value depends only on the nature of the substance not amount of substance

ΔQ = Amount of heat energy

ΔT = Change in temperature

m = Mass of the substance

The SI unit for specific heat capacity is J kg-1K-1. Heat capacity and specific heat capacity are always positive quantities.


From the table it is clear that water has the highest value of specific heat capacity. For this reason it is used as a coolant in power stations and reactors.

When we study properties of gases, it is more practical to use molar specific heat capacity. Molar specific heat capacity is defined as heat energy required to increase the temperature of one mole of substance by 1K or 1°C. It can be written as follows


Here C is known as molar specific heat capacity of a substance and μ is number of moles in the substance.

The SI unit for molar specific heat capacity is J mol-1K-1 . It is also a positive quantity.

 

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