Ch20; Heat and the First Law of Thermodynamics
Work and Heat
in Thermodynamic Processes
Work Done by a Gas
When a gas expands it does work on its surroundings. That work is equal to the area under the curve on a P-V diagram which describes that expansion.
When a gas is compressed, work is done on the gas by its surroundings. We can also say the gas does negative work on its surroundings. Again, the work is equal to the area under the curve on a P-V diagram which describes that compression.
Isobaric process:Process at constant pressure:
W = F D
W = ( F / A ) ( A D )
W = P ( A D )
W = P (
V)
Work = area under the curve on a P-V diagram.
Work = area under the curve on a P-V diagram -- even if the process is not isobaric.
This provides a nice example of calculus.
The work done is the area under the curve on a P-V diagram. This means the work done depends upon the path taken. Taking a system from some initial state to some final state along different "paths" means that different amounts of work will be done.
Return to Ch20 ToC (c) Doug Davis, 2002; all rights reserved
