Thermodynamics Test #3
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In a T-S diagram a line of constant enthalpy
- has a negative slope in the superheated vapor region.
- has a negative slope in the liquid-vapor region.
- has a zero slope for ideal gases.
The entropy of an ideal gas
- increases with decreasing pressure.
- increases with increasing temperature.
- depends on both pressure and temperature.
The entropy change for a reversible process
- is the same as the entropy change of an irreversible process.
- depends only on the initial and final state.
For a real process the entropy change of the UNIVERSE
will always be greater than zero.
An ideal gas expands at constant temperature.
The entropy increases because the volume increases.
whenever TWO substances at DIFFERENT temperatures are in contact
- there will be heat transfer from the hot to the cold substance.
- there will be an increase in the total entropy of the universe due to the heat transfer.
- the process will be irreversible.
The entropy of a closed system can increase because of
- heat transfer into the system.
- entropy production in the system
The entropy production, s, in a CLOSED system is always
zero if the process is reversible.
For a closed system undergoing an irreversible process the entropy is always..
The Carnot Cycle (all of the above)
- can be considered to be either a work producing cycle or a work consuming cycle.
- is an idealization of all power cycles.
- has a thermal efficiency that is based only on the temperatures of the reservoirs.
consider TWO processes between state A and B. The entropy must ..
- be the same for both paths.
- be equal
Consider a closed system undergoing a process from state A to B. The entropy change of the system at state A must be
the same regardless if reversible or irreversible.
Consider an isolated system containing two regions both filled with air and separated by a partition. The two regions are initially at different temperatures but because of heat transfer through the partition, the gases eventually reach the same temperature. The entropy of the system would:
Do irreversible or reversible processes produce more work at constant temperature.
Irreversible processes produce less work!
When someone says "Entropy always increases." what they really should say is;
The entropy of the system plus the entropy of the surroundings always increases.
consider two REVERSIBLE processes between the same two states. The two processes will have the same:
- entropy change.
- heat transfer.
Consider a device that has a single inlet and a single exit operating at steady state with known inlet and exit states. The specific entropy at the exit minus the specific entropy at the inlet:
Only depends on the inlet and exit states!
on a TS diagram for a steam turbine:
- the exit state will be directly below the inlet state if the turbine is isentropic.
- the area under the curve is the heat transfer if the turbine is internally reversible.
the entropy change of an ideal gas depends on;
a process will be isentropic if;
if it is adiabatic and reversible
Isentropic efficiency of an adiabatic compressor;
(IDEAL/ACTUAL) - enthalpy change
The integral for the TdS is equal to;
- Heat transfer only if the process is reversible.
For a constant pressure ideal gas process, the specific heat is always;
not constant ha
a line of constant pressure in a T-S diagram has a ______ slope in the _________ region
Positive, Superheated Vapor
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