Configuration Work
This is the work done in a reversible process given by the product of some
intensive variable (y) and the change in some extensive variable (X). The most
general case would be:
đW 
 y dX ,
i
i
i  1,2,....n.
i
• đW is called the configuration work; it is an inexact differential, i.e. work is
not a state variable.
• The amount of work done changing the configuration of a system from one
state to another depends on how the work is done, i.e. on the path taken
between the final and initial states. The path must be specified in order to
calculate work via integration.
• By convention, đW is the work done on ‘the system’. Thus, as an example, đW
is positive when a gas is compressed.
Configuration Work
This is the work done in a reversible process given by the product of some
intensive variable (y) and the change in some extensive variable (X). The most
general case would be:
đW 
 y dX ,
i
i
i
i  1,2,....n.
Dissipative Work
• This is the work done in an irreversible process; it is always done ‘on the
system’.
• Total work is the algebraic sum any configuration work and any dissipative
work.
• If a process is reversible, then dissipation is necessarily zero.
Examples: Stirring
Resistive electrical heating
Frictional work
Plastic deformation
Many chemical reactions
Joule’s apparatus for measuring the mechanical equivalent of heat
1 cal = 4.184 J will raise temperature of water by 1 C (14.5 C to 15.5 C)
More on specific heat
Using the first law, it is easily shown that:
 đq   u 
cv  
 

dT

T

v 
v
•Finding a similarly straightforward expression for cP is not as easy, and
requires knowledge of the state equation.
•For an idea gas, the internal energy depends only on the temperature of the
gas T. Therefore,
du
cv 
dT
and
T
u  u0   cv dT
T0
•These are far more useful expressions than the original definition of specific
heat.