Sunday, 15 December 2019

Heat Capacity Vs Specific Heat

  Daman       Sunday, 15 December 2019
Heat Capacity Vs Specific Heat -  We all know that each substance is made up of molecules. The molecules in a substance are in a state of random motion. 

Before the comparison of heat capacity and specific heat, certain things you must learn and bear mind.


  • The kinetic energy due to the random motion of molecules of a substance is known as its heat energy. Thus, each body possesses heat energy in the form of its internal kinetic energy.



  • When some quantity of heat is supplied to a body, the random molecular motion increases, which results in an increase in average internal the kinetic energy of its molecules and hence the joule increase in its temperature. 


  • Similarly, if some quantity of heat is removed (or withdrawn) from a body, its random molecular motion decreases so It is the average internal kinetic energy of the body decreases and the temperature of the body falls.


Heat Capacity Vs Specific Heat

 
Heat Capacity Vs Specific Heat

When two bodies at different temperatures are in contact, heat flows from the body at a higher temperature to the body at a lower. Thus, it is the temperature that determines the direction of the flow of heat.

The quantity of heat energy required to raise the temperature of a body depends on three factors
  •  Mass of the body
  •  Material for substance and 
  •  Rise in temperature of the body.

Experimentally it is found that



  • Different masses of the same substance require different amounts of heat energy to raise their temperature by the same amount. The amount of heat energy required is found to be directly proportional to the mass of the substance i.e.,
 Q ∝ mass


  •  Equal masses of the different substances require different amounts of heat energy to raise their temperature by the same amount. For example, if masses of water and copper are heated through 1°C, the amount of heat required for nearly ten times the heat required for copper. Thus, the amount of heat energy required depends on the nature (or characteristic) of the substance and it is expressed in terms of its specific heat capacity c. 


  • Equal masses of the same substance require different amounts of heat energy to raise their temperature by different amounts. The amount of heat energy required is found to be directly proportional to the rise in temperature Δt i.e.
 (Δ means - Change in quantity)
Q Δt
  • From above, Q m and Q At
    or  Q = c m Δt

    where c is the constant of proportionality which is called the specific heat capacity of the substance. It is the characteristic of the substance.

Heat Capacity

 

From our everyday experience, we find that different bodies require different amounts of heat energy for an equal rise in their temperature.

This property of a body is expressed in terms of its heat capacity. The heat capacity of a body is defined as follows:

The heat capacity of a body is the amount of heat energy required to raise its temperature by

1°C  or 1K.



Heat Capacity 


-or -


Heat Capacity formula 


In other words, a 1°C rise in temperature is the same as 1 K rise in temperature.

Units of Heat Capacity

 

The S.I. unit of heat capacity is joule per kelvin (or J/ K). It is also written as joule per degree C (or J/ °C).

The other common units of heat capacity are calorie °C-1 (or cal K-1) and kilo-calorie/ °C (or kilo-calorie K-1). They are related as



Heat Capacity units


If the heat capacity of a vessel is 30 J/K, it k means that the heat energy required to raise the temperature of that vessel by 1 K is 30 J.



Specific Heat


The heat capacity of a body when expressed for unit mass is called its specific heat capacity. It is denoted by the symbol C. Thus, the specific heat of a substance (or a body) is defined as the heat capacity per unit mass of that body, i.e.,

Specific Heat




The above equation relates the heat capacity of a body to the specific heat capacity of its material.

In other words, we can define specific heat capacity as follows:

The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of a unit mass of that substance through 1°C (or 1K).






Units of Specific Heat

 

The S.I. unit of specific heat capacity is joule per kilogram per kelvin ( or J/ kg K) or joule per kilogram per degree celsius (or J/ kg °C).

The other units of specific heat capacity are cal/ g °C and kilo-cal /kg °C. These units are related as :

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If the specific heat capacity of copper is 0.4 J/gK, it means that the heat energy required to raise the temperature of 1 g of copper by 1 K (or 1°C) is 0.4 J.

 

Heat Capacity Vs Specific Heat

 

Heat Capacity Specific Heat
 It is the amount of heat energy required to raise the temperature of an entire mass of the body by 1°C.  It is the amount of heat energy required to raise the temperature of a unit mass of the body by 1°C.
It depends on the material and mass of the body. More mass of the body more is its heat capacity. It does not depend on the mass of the body. It is characteristic of the material body.
Its unit is J per K ( J K-1)  Its unit is J kg-1 K-1
Heat capacity =mass x Specific heat capacity Specific heat Capacity = Heat capacity/mass m


The specific heat capacity of a substance is its characteristic property. It is different for different substances. If we heat equal masses of two different substances on the same burner so that the rate of heat supply is time, we notice that after the same interval, the rise in temperature for the two substances is different. This is due to their different specific heat capacities. The substance of low specific heat capacity will show a greater rise in temperature. Water has an unusually high specific heat capacity (= 4200 J/ kg K).

Note


The specific heat capacity changes with the change in phase of the substance. The specific heat capacity of water is 4200 J/ kg K, of ice is 2100 J per kg per K and of steam is 460 J per kg per K.

The specific heat capacity is maximum for with so hydrogen (c = 14630 J kg-1 K-1).


Substance Specific Heat (J/Kg k
Lead 130
mercury 139
Brass 380
Zinc 391
Copper 399
Iron 483
Glass 504
Aluminum 882
Kerosene 2100
Ice 2100
Sea Water 3900
Water 4180


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