About Lesson
HEAT CAPACITY
if you Heat the same bodies to different temperatures and drop it into identical calorimeters containing the same amount of water, you will observe that they attain different final temperatures. The heat capacity, C, of an object is the quantity of heat which must be transferred to it to give it one-degree rise in temperature.
Bodies of different masses, of the same material and at the same temperature have different amount of heat. The specific heat capacity of a substance is defined as the amount of heat energy required to raise the temperature of a unit mass of a substance by 1 °C or 1K. It is used to describe the heat capacity of a substance per unit mass. The SI unit for the specific heat capacity ‘c’ is J∙kg^(-1)∙℃^(-1) or J∙kg^(-1)∙K^(-1) (or simply J/kg∙°C and J/kg∙K). It is given by the relation: Q=mc∆T. The specific heat capacity can be found experimentally in the laboratory using two different methods, namely, the electrical method and the method of mixture.
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LATENT HEAT
Latent heat is that heat that does not show its presence in terms of a change in temperature. It is the amount of heat that is absorbed by an object in order to undergo a change of state. Whenever energy is transferred between a substance and its surroundings, the substance undergoes a change in temperature. The latent heat of fusion of a substance is the amount of heat the substance requires (absorbs) to change its state from solid to liquid at a constant temperature.
The specific latent heat of fusion of a substance is the amount of heat energy required to change unit mass (1kg) of the substance from solid to liquid without change of temperature. The symbol for specific latent heat of fusion is Lf and it SI unit is joule per kilogram (J/kg).
Specific latent heat=(heat energy)/mass
Then the heat energy Q or E_L supplied to cause a change of state of a solid; mass m is given by Q = mLf
Latent heat of vaporisation of a substance is the amount of heat energy required (absorbed) by the substance to change its state from liquid to gas at a constant temperature. The specific latent heat of vaporisation of a substance is the heat energy required to change a unit mass of a substance from liquid to gas without change in temperature. The symbol for specific latent heat of vaporisation is LV and its SI unit is J/kg.
The heat energy Q supplied to cause change of state of mass m of a liquid to gas is given by Q = mLv
Note: the specific latent heat of vaporisation of steam is the quantity of heat energy required to change 1 kg of water at 100°C to 1kg of steam at100°C.
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