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10.2 The First Law of Thermodynamics

The First Law of Thermodynamics is the law of conservation of energy. It can be stated in various ways as follows :

  1. Energy can neither be created nor destroyed although it can be converted from one form into another.

  2. Whenever a quantity of one form of energy disappears, an equivalent amount of energy of another kind makes its appearance.

  3. The total energy of an isolated system remains constant whatever changes may take place in the system.

  4. It is not possible for any machine to produce work without consuming energy.

  5. The energy of the universe remains constant.

Mathematical Expression of the First Law of Thermodynamics

Let q be the heat absorbed by a system. Part of it may be utilized for increasing the internal energy i.e. DE.

DE = E2 - E1

and part for external work.

According to the first law of thermodynamics, the total energy of a system remains constant.


Heat absorbed = Energy change + work done

 q = DE + W

\ DE = q - W

If work W is only pressure - volume type

W = P D V

\ DE = q - P D V or q = DE + P D V


Index

10.1 Introduction
10.2 First Law of Thermodynamics
10.3 Enthalpy
10.4 Second Law of Thermodynamics
10.5 Gibb's Free Energy
10.6 Absolute Entropies

Chapter 11





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