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15 Thermodynmics 250 272 Final Essay

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Thermodynamics deals with the relation between heat energy and other forms of energy.


The thermodynamics coordinates of a system which are also called state variables are pressure, volume and temperature which are inter dependent.


The temperature of a system can be expressed as a function of pressure and volume is f(P, V)=T.


Calorimetery is the study of the measurement of quantities of heat.


Quantity of heat is the amount of molecular energy stored in a body.


Calorie : The quantity of heat required by one gram of water to raise its temperature from 14.5°C to 15.5°C is called one calorie.


British Thermal Unit : The amount of heat required by 1 Pound of water to raise its temperature by 1°F is called one British thermal unit.


Pound calorie : The amount of heat required by
1 Pound of water to raise its temperature by 1°C is called one pound calorie. 1 pound calorie=453.6 calories
1 calorie=4.186 joule

Heat Capacity :

The amount of heat required to produce a specified change of temperature is directly proportional to the mass of the material.

10. For a given mass of material, the amount of heat absorbed is directly proportional to the temperature increase.
11. The amount of heat required to raise the temperature of the whole body by 1°C is called heat capacity or thermal capacity. Unit is J/K or Cal/°C.

12. Specific heat : The quantity of heat required by one gram of a substance to raise its temperature by 1°C is called its specific heat.
Heat capacity per unit mass. Unit is J/Kg-K or Cal/g-°C.
dQ = msdT
13. If m is the mass and s is the specific heat of the material of the body, then the thermal capacity = ms cal/°C.
14. Of all solids and liquids, water has the highest specific heat or specific heat capacity. The value is 1 cal/g/°C or 4200 J/kg/K.
15. The specific heat of lead is the least among solids. (i.e., 0.03 cal/g/°C) 16. In liquids, mercury has least specific heat.

17. Of all solids, liquids and gases, hydrogen has the highest specific heat. It is equal to 3.5 cal/g/°C. 18. Specific heat depends upon the nature of the substance and does not depend upon mass, volume and heat supplied.

19. Specific heat of copper

= 0.1 cal/g/°C.

Specific heat of ice

= 0.5 cal/g/°C

Specific heat of steam

= 0.45 cal/g/°C

Specific heat of lead

= 0.03 cal/g/°C.

20. Specific heat of a solid at its melting point is infinite. 21. Specific heat of a liquid at its boiling point is infinite. 22. The water equivalent of a body is the number of grams of water which require the same amount of heat as the substance for the same rise of temperature. Unit is grams. Water equivalent=ms grams.

23. Water equivalent is numerically equal to heat capacity.
24. Latent heat (L) is the quantity of heat required by unit mass of a substance to change its state at a constant temperature. Unit of L is cal/g or J/kg.
25. Latent heat of fusion is the quantity of heat required by unit mass of a solid to melt it at its melting point.
26. The latent heat of ice is 80 cal/g or 3.35x105 J/kg.
27. Latent heat of vapourisation is the quantity of heat required by unit mass of a liquid to vapourise it at its boiling point.
28. The latent heat of steam is 540 cal/g or 2.26x106 J/kg.
29. Latent heat of vapourisation of water decreases with the increase of pressure (i.e., increase of boiling point).
30. The latent heat of steam at boiling point t is given by L=600−0.06t. 31. Latent heat of vapourisation decreases with increase in temperature. 32. Latent heat of a substance becomes zero at critical temperature. 33. Latent heat depends on the nature of a substance and pressure. 34. During the change of state, the formula used to calculate the heat lost or heat gained is Q = mL. 35. When one gram of steam at 100°C is mixed with one gram of ice at 0...

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