Thermo Final Exam - Conceptual Problems
A property whose value for an overall system is the sum of its values for the parts into which the system is divided
Extensive property
At liquid states, the following approximation is reasonable for many engineering applications: s(T,p) ≈ sg(T).
False
T/F: A vessel holding 0.5 kg of oxygen (O2) contains 16 lb of O2.
False
T/F: For an ideal gas with constant specific heats, the entropy is constant.
False
T/F: Mass is an intensive property.
False
T/F: Temperature is an extensive property.
False
T/F: The composition of a closed system cannot change.
False
T/F: The entropy of a fixed amount of an ideal gas increases in every isothermal process.
False
T/F: The pound force, lbf, is equal to the pound mass, lb.
False
Saturated water vapor at 5 bar undergoes a process in a closed system to a final state where the pressure is 10 bar and the temperature is 200°C. Can the process occur adiabatically?
No
The specific internal energy of an ideal gas depends on temperature alone. Is the same statement true for specific entropy of an ideal gas?
No
True/False: A closed system can experience a decrease in entropy only when there is heat transfer from the system to its surroundings during the process.
True
True/False: For a specified inlet state, exit pressure, and mass flow rate, the power developed by a turbine operating at steady state is less than if expansion occurred isentropically.
True
True/False: For an incompressible substance, the specific entropy is a function of temperature alone.
True
True/False: For an internally reversible, steady-state flow process, the heat transfer per unit mass can be represented as the area below the process line on a T-s diagram.
True
True/False: If air leaks slowly from a well-insulated tank, the air that remains in the tank can be modeled as undergoing an isentropic process.
True
True/False: In an adiabatic and internally reversible process of a closed system the entropy remains constant.
True
True/False: In statistical thermodynamics, entropy is associated with the notion of microscopic disorder.
True
True/False: Interactive Thermodynamics: IT employs the approximation given in Eq. 6.5 for the specific entropies of liquids.
True
True/False: The Carnot cycle is represented on a T-s diagram as a rectangle.
True
True/False: The TⅆS equations are fundamentally important in thermodynamics because of their use in deriving important property relations for pure, simple compressible systems.
True
True/False: The change in entropy of a closed system is the same for every process between two specified states.
True
True/False: The entropy change of a closed system during a process can be greater than, equal to, or less than zero.
True
True/False: The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.
True
True/False: The specific internal energy and enthalpy of an ideal gas are each functions of temperature alone, but its specific entropy depends on two independent intensive properties.
True
True/False: When a system undergoes a Carnot cycle, no entropy is produced within the system.
True
True/False: When applying the second law to closed systems, energy balances, property relations, and property diagrams often are used in conjunction with the entropy balance.
True
A gas flows through a one-inlet, one-exit control volume operating at steady state. Heat transfer at a rate Qcv takes place at a location on the boundary where the temperature is Tb. Internal irreversibilities present, Qcv ≥ 0 Is the specific entropy at the exit is greater than, equal to, or less than the specific entropy of the gas at the inlet?
greater than
A gas flows through a one-inlet, one-exit control volume operating at steady state. Heat transfer at a rate Q˙cv takes place at a location on the boundary where the temperature is Tb. No internal irreversibilities, Qcv > 0 Is the specific entropy at the exit is greater than, equal to, or less than the specific entropy of the gas at the inlet?
greater than
A closed system undergoes a process in which work is done on the system and heat transfer Q occurs only at a location on the boundary where the temperature is Tb. Internal irreversibilities present, Q < 0 Is the entropy change of the system is positive, negative, zero, or indeterminate?
indeterminate
A special type of closed system that does not interact in any way with its surroundings is an __________.
isolated system
A gas flows through a one-inlet, one-exit control volume operating at steady state. Heat transfer at a rate Q˙cv takes place at a location on the boundary where the temperature is Tb. No internal irreversibilities, Qcv < 0 Is the specific entropy at the exit is greater than, equal to, or less than the specific entropy of the gas at the inlet?
less than
The reference state for specific entropy of water in Tables A-2 through A-6 is that specific entropy is set to zero at saturated _____________, 0 C.
liquid
A closed system undergoes a process in which work is done on the system and heat transfer Q occurs only at a location on the boundary where the temperature is Tb. Internally reversible process, Q < 0 Is the entropy change of the system is positive, negative, zero, or indeterminate?
negative
A system is at steady state if...
none of its properties changes with time
A closed system undergoes a process in which work is done on the system and heat transfer Q occurs only at a location on the boundary where the temperature is Tb. Internally reversible process, Q > 0 Is the entropy change of the system is positive, negative, zero, or indeterminate?
positive
The isentropic turbine and compressor efficiencies are defined from a fixed initial state to a specified final ___________.
pressure
Ammonia undergoes an isentropic process from an initial state at 10 bar, 40C to a final pressure of 3.5 bar. In which region is the final state: superheated vapor or the two-phase liquid-vapor?
two-phase liquid-vapor
A fixed quantity of matter that is under study. There can be no transfer of mass across its boundary.
Closed system
A region of space through which mass may flow
Control volume
True/False: A nozzle can be modeled as a throttling process.
False
True/False: A process that violates the second law of thermodynamics violates the first law of thermodynamics.
False
True/False: At liquid states, the following approximation is reasonable for many engineering applications: s(T,p) ≈ sg(T)
False
True/False: Entropy is produced in every internally reversible process of a closed system.
False
True/False: For a specified inlet state, exit pressure, and mass flow rate, the power input to a compressor operating adiabatically and at steady state is less than what would be required if the compression occurred isentropically.
False
True/False: For an ideal gas with constant specific heats, the entropy is constant.
False
True/False: The only entropy transfers to or from control volumes are those accompanying heat transfer.
False
True/False: The steady-state form of the control volume entropy balance requires that the total rate at which entropy is transferred out of the control volume be less than the total rate at which entropy enters.
False (greater than the total rate at which entropy enters)
A property whose value is independent of the size or extent of a system and may vary from place to place within the system at any moment
Intensive property
A closed system undergoes a process for which S2 = S1. Must the process be internally reversible?
No
T/F: 1 N equals 1 kg·m/s^2 but 1 lbf does not equal 1 lb·ft/s^2.
True
T/F: A closed system always contains the same matter; there is no transfer of matter across its boundary.
True
T/F: For an incompressible substance, the specific entropy is a function of temperature alone.
True
T/F: Heat transfer for internally reversible processes of closed systems can be represented as areas on T-s diagrams.
True
T/F: If a system is isolated from its surroundings and no changes occur in its observable properties, the system was in equilibrium at the moment it was isolated.
True
T/F: If the value of any property of a system changes with time, that system cannot be at steady state.
True
T/F: Pressure is an intensive property.
True
T/F: Specific volume, the volume per unit of mass, is an intensive property whereas volume and mass are extensive properties.
True
T/F: The Tⅆ equations are fundamentally important in thermodynamics because of their use in deriving important property relations for pure, simple compressible systems.
True
T/F: The change in entropy of a closed system is the same for every process between two specified states.
True
T/F: The choice of system, boundary, and surroundings is arbitrary and depends on the convenience it allows in the subsequent analysis.
True
T/F: The specific internal energy and enthalpy of an ideal gas are each functions of temperature alone, but its specific entropy depends on two independent intensive properties.
True
T/F: Volume is an extensive property.
True
T/F: When a closed system undergoes a process between two specified states, the change in temperature between the end states is independent of details of the process.
True
In the limit, is it possible for a process of a closed system to be internally reversible, while irreversibilities exist within the surroundings?
Yes
Whenever heat transfer occurs for a closed system, there is a corresponding entropy transfer. Are the directions the same?
Yes
According to the increase of entropy principle, is it possible for the entropy of a system to increase?
Yes
Entropy change is evaluated using Eq. 6.2a based on an internally reversible process. Can the entropy change between two states of a system be determined for any process linking the two states whether reversible or not?
Yes
For phase change of water from saturated liquid to saturated vapor at constant pressure in a closed system, can the change in specific enthalpy be determined if the change in specific entropy is known?
Yes
A control volume is a system that...
allows a transfer of matter across its boundary
When a system is isolated, a) its mass remains constant b) its temperature may change c) its pressure may change d) all of the answers are correct
d) all of the answers are correct
The list consisting only of intensive properties is a) volume, temperature, pressure b) mass, temperature, pressure c) specific volume, mass, volume d) pressure, temperature, specific volume
d) pressure, temperature, specific volume
Carbon dioxide as an ideal gas undergoes a process at constant temperature from 10 lbf/in.2 to 50 lbf/in.2 Does the specific entropy of the gas increase, decrease, or stay constant?
decrease
Carbon dioxide as an ideal gas undergoes a process at constant temperature from 10 lbf/in^2 to 50 lbf/in^2 Does the specific entropy of the gas increase, decrease, or stay constant?
decrease
The expression p2/p1 = (T2/T1)^k/(k-1) relates two states of an ideal gas with constant specific ratio k and equal __________.
entropy
A gas flows through a one-inlet, one-exit control volume operating at steady state. Heat transfer at a rate Q˙cv takes place at a location on the boundary where the temperature is Tb. No internal irreversibilities, Qcv = 0 Is the specific entropy at the exit is greater than, equal to, or less than the specific entropy of the gas at the inlet?
equal to
A closed system undergoes a process in which work is done on the system and heat transfer Q occurs only at a location on the boundary where the temperature is Tb. Internally reversible process, Q = 0 Is the entropy change of the system is positive, negative, zero, or indeterminate?
zero