Chapter 4 Flashcards
The expansion and compression work in a piston-cylinder device
Moving boundary work (P dV work)
A process during which the system remains nearly in equilibrium at all times
Quasi-equilibrium process
Wb is positive for ____
Expansion
Wb is negative for ____
Compression
The work associated with a moving boundary is called _____
Boundary work
The boundary work done during a process depends…
On the path followed as well as the end states
The area under the process curve on a P-V diagram represents the _____
Boundary work
The area under the process curve on a P-V diagram is equal, in magnitude, to…
The work done during a quasi-equilibrium expansion or compression process of a closed system
The net work done during a cycle
The difference between the work done by the system and the work done on the system
What is the boundary work for a constant volume process?
Wb=0
Boundary work done during _____ is always zero
A constant volume process
Energy balance when sign convention is used
Heat input and work output are positive
Heat output and work input are menegative
Stationary system: energy balance
Q-W = change in U
Work done on the system
Negative
Work done by the system
Positive
Closed system undergoing a quasi-equilibrium process
P = constant process energy balance
Not valid for closed systems processes
Expansion against a vacuum
Involves no work and no energy transfer
The energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant
Specific heat at constant volume (cv)
The energy required to raise the temperature of the unit mass of a substance by one degree as the pressure is maintained constant
Specific heat at constant pressure (cp)
The specific heat of a substance changes with _____
Temperature
Cv and Cp are ____
Properties
The change in internal energy with temperature at constant volume
Cv
The change in enthalpy with temperature at constant pressure
Cp
Cp is always greater than Cv. True or False?
True
At low pressures, all real gases approach behavior, and therefore their specific heats depend on ____ only
Temperature
The specific heats of real gases at low pressures are called ____
Ideal gas specific heats, zero-pressure specific heats (Cp0, Cv0)
Specific heat ratios of monatomic gases
It’s value is essentially constant at 1.667
Specific heat ratios for diatomic gases
1.4 at room temperature
Specific heat ratio varies with _____
Temperature
A substance whose specific volume (or density) is constant
Incompressible substance
Solids and liquids
Cv=Cp
Specific volumes remain constant
Liquids at constant pressure
Heaters
Liquids at constant temperature
Pumps
