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Heat Transfer

In order to increase the temperature of a substance, we have to supply heat. The heat that should be supplied to increase the temperature varies from one substance to another. So scientists have come up with a way to define this - the specific heat. The specific heat (J/g.Co) of a substance is the amount of heat that should be added to one gram of that substance to raise its temperature by one degree Celsius. The Heat capacity of a given sample substance is the amount of heat that is required to increase the temperature by one degree Celsius. Heat capacity, specific heat, and temperature are related according to the following relations:
 

q = C (tf– ti) = CΔt, 

where q is the heat required,

C is the heat capacity, and

Δt is the change in temperature.

 

q = m CspΔt, 

where q is the heat required,

m is the mass of the substance in grams,

Csp is the specific heat, and

Δt is the change in temperature.

 

Let's now talk about the temperature change when heat is added to a substance - the changes in temperature that occur during the change of a substance from its solid state to gaseous state or vice versa. It is easier to understand this from the Figure 7-4.
 
Let's say we are adding heat to a substance which is in its solid state. As the heat increases, the temperature increases until the melting point is attained. Then the temperature will not rise until the substance has melted. Keep in mind that the process of melting requires energy. As more heat is supplied, the temperature again starts increasing until the boiling point has been reached. Then again the temperature will not rise during the process of boiling or vaporization, because the energy that is supplied is used for the process of vaporization. After vaporization is completed, as more heat is supplied, the temperature again starts increasing.
 

 

Some related terms:
Heat of fusion of a solid substance is the quantity of heat required to melt one gram of that substance at its melting point. The usual unit used is J/g.
Heat of vaporization of a liquid substance is the quantity of heat required to vaporize one gram of that substance at its boiling point. The unit used is J/g.
Heat of condensation of a substance is the quantity of heat that should be removed to condense one gram of that substance at its condensation point. The unit used is J/g.
Heat of crystallization of a substance is the quantity of heat that should be removed to crystallize one gram of that substance at its freezing point. The unit used is J/g.





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