A fixed mass of an ideal gas has a volume 
and a pressure 
. The gas undergoes a cycle of changes, X to Y to Z to X, as shown in the figure below.
The first law of thermodynamics for a system may be represented by the equation
State, with reference to the system, what is meant by:
: ...........................................
: .....................................................
: ......................................................
Explain how the first law of thermodynamics applies to the change Z to X.
