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 :
- Energy can neither be created nor destroyed although it can be converted
from one form into another.
- Whenever a quantity of one form of energy disappears, an equivalent
amount of energy of another kind makes its appearance.
- The total energy of an isolated system remains constant whatever changes
may take place in the system.
- It is not possible for any machine to produce work without consuming
energy.
- 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.
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 |
|
