Introduction to Heat Capacity and Principle of Calorimetry | Physics Grade XI

Heat Capacity

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Introduction to Heat Capacity and Principle of Calorimetry | Physics Grade XI

Introduction to Heat Capacity and Principle of Calorimetry

Calorimetry: Calorimetry is an experimental technique for quantitative measurement of heat exchange.

CalorimeterCalorie is the unit heat in CGS-system and joule in SI-units. One calorie is the amount of heat necessary to rise the temperature of one gram of water from 14.50C to 15.50C. One calorie is equal to 4.2 joule.

Specific heat capacity
When a body is heated, its temperature rises. Consider two different bodies and they are heated at the same rate by a burner for equal time. We will observe that the temperature of the two bodies will not be the same. So, the amount of heat required to raise the temperature depends upon different factors.
 
It is observed that the amount of heat Q required to raise the temperature of a substance is directly proportional to its mass, m
     Q α m ….... (i)
And is directly proportional to the rise in temperature, Δθ
     Q αΔθ ….... (ii)
Combining equation (i) and (ii), we have
     Q α m. Δθ
     or, Q = m. s. Δθ ….... (iii)
Where s is a proportionality constant called the specific heat capacity of the substance.
 
If m= 1kg and Δθ = 10C, then
     Q = s
 
Thus, the specific heat capacity of a substance is defined as the amount of heat required to increase the temperature of unit mass of substance through one degree. So,
     s = Q/(m Δθ)
Its unit is J kg-1K-1 in SI-systems and Calg-10C-1 in CGS system. Specific heat capacity of water is 1 Cal g-10C-1 or 4200 J kg-1K-1.
 
Heat Capacity or Thermal Capacity
Heat capacity of a substance is defined as the amount of heat required to increase its temperature through one degree. It also called thermal capacity. If Q is the amount of heat required to change the temperature of a body of mass m through Δθ, then
     Q = m. s. Δθ
 
If the temperature difference, Δθ = 10C, then
     Q = m. s
This quantity of heat is the heat capacity which is equal to the product of mass and specific heat capacity. Its unit is J K-1 in SI-units Cal C-1 in CGS system
 
Water equivalent of a substance
It is the mass of water that will absorb or lose the same quantity of heat as the substance for the same change in temperature.
 
Principle of Calorimetry
When two substances at different temperatures are mixed together, the hot substance loses heat while the cold substance gain heat. If there is no loss of heat in the surrounding, the total amount of heat lost by the hot substance is equal to the amount of heat gained by the cold substance.
     i.e; heat lost = heat gained

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