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Questions and Answers
What does the equation $ein - eout = Δesystem$ represent in the context of a constant-volume process?
What does the equation $ein - eout = Δesystem$ represent in the context of a constant-volume process?
- The net amount of energy transferred to the system. (correct)
- The change in pressure of the system.
- The change in mass during the process.
- The total work done by the system.
In a constant-pressure expansion or compression process, what can the PV terms be associated with?
In a constant-pressure expansion or compression process, what can the PV terms be associated with?
- The internal energy of the substance. (correct)
- The change in temperature of the substance.
- The work done on or by the system.
- The heat capacity at constant volume.
What is the specific heat at constant volume denoted as?
What is the specific heat at constant volume denoted as?
- cv (correct)
- w
- cp
- c
Which of the following statements about specific heats is true?
Which of the following statements about specific heats is true?
What is the unit of measurement for specific heats?
What is the unit of measurement for specific heats?
What condition must be met for the pressure at the inner surface of the piston to equal the pressure of the gas in the cylinder?
What condition must be met for the pressure at the inner surface of the piston to equal the pressure of the gas in the cylinder?
Which of the following statements is true regarding boundary work during an expansion process?
Which of the following statements is true regarding boundary work during an expansion process?
How is boundary work characterized in the context of a constant-volume process?
How is boundary work characterized in the context of a constant-volume process?
What must the energy transferred as work from the system equal during an expansion in a car engine?
What must the energy transferred as work from the system equal during an expansion in a car engine?
In non-quasi-equilibrium processes, what pressure is used for calculating boundary work?
In non-quasi-equilibrium processes, what pressure is used for calculating boundary work?
Which of the following processes allows the use of the boundary work relation for solids and liquids?
Which of the following processes allows the use of the boundary work relation for solids and liquids?
What happens if the process is isobaric?
What happens if the process is isobaric?
In energy conservation, what does the boundary work performed by the system represent?
In energy conservation, what does the boundary work performed by the system represent?
What primarily influences the Internal Energy of an ideal gas?
What primarily influences the Internal Energy of an ideal gas?
What conclusion did Joule reach regarding the Internal Energy of Air during his experiment?
What conclusion did Joule reach regarding the Internal Energy of Air during his experiment?
For low-density gases, what is the relation between Internal Energy and pressure?
For low-density gases, what is the relation between Internal Energy and pressure?
What properties can the Specific Heat at constant volume (cv) and constant pressure (cp) of an ideal gas be attributed to?
What properties can the Specific Heat at constant volume (cv) and constant pressure (cp) of an ideal gas be attributed to?
In Joule's experiment, what does it indicate when there was no change in the temperature of the water bath?
In Joule's experiment, what does it indicate when there was no change in the temperature of the water bath?
Which of the following statements is true for an ideal gas under ideal conditions?
Which of the following statements is true for an ideal gas under ideal conditions?
As the density of a gas decreases, how does its dependence of Internal Energy on pressure change?
As the density of a gas decreases, how does its dependence of Internal Energy on pressure change?
Which of the following factors does NOT affect the Internal Energy of an ideal gas?
Which of the following factors does NOT affect the Internal Energy of an ideal gas?
What is the behavior of real gases at low pressures?
What is the behavior of real gases at low pressures?
What is another term for the specific heats of real gases at low pressures?
What is another term for the specific heats of real gases at low pressures?
What primarily causes the variation of specific heat with temperature in gases?
What primarily causes the variation of specific heat with temperature in gases?
How do specific heats of complex molecules behave with temperature?
How do specific heats of complex molecules behave with temperature?
Which method is considered the easiest and most accurate for calculating changes in internal energy and enthalpy?
Which method is considered the easiest and most accurate for calculating changes in internal energy and enthalpy?
Which temperature is often chosen as the Reference Temperature when preparing ideal gas tables?
Which temperature is often chosen as the Reference Temperature when preparing ideal gas tables?
What is true about the variation of Cp with temperature?
What is true about the variation of Cp with temperature?
What happens to internal energy and enthalpy when specific heat is taken constant over a range?
What happens to internal energy and enthalpy when specific heat is taken constant over a range?
What is the primary method of calculating specific heats when property tables are not available?
What is the primary method of calculating specific heats when property tables are not available?
What is the significance of the specific heat ratio for monatomic gases?
What is the significance of the specific heat ratio for monatomic gases?
Which statement about average specific heats is true?
Which statement about average specific heats is true?
In the context of an ideal gas, what is the relationship between internal energy change and specific heat?
In the context of an ideal gas, what is the relationship between internal energy change and specific heat?
What pressure is required to move the piston in the given example?
What pressure is required to move the piston in the given example?
How does the specific heat ratio of diatomic gases compare to that of monatomic gases at room temperature?
How does the specific heat ratio of diatomic gases compare to that of monatomic gases at room temperature?
What happens to the specific heat values when a gas is heated in the example?
What happens to the specific heat values when a gas is heated in the example?
What is one reason for the convenience of computerized calculations over hand calculations for specific heats?
What is one reason for the convenience of computerized calculations over hand calculations for specific heats?
What characterizes an incompressible substance?
What characterizes an incompressible substance?
In the analysis of internal energy and enthalpy changes for solids, what assumption can be made about the term v ΔP?
In the analysis of internal energy and enthalpy changes for solids, what assumption can be made about the term v ΔP?
For which type of process does the equation Δh = v ΔP apply?
For which type of process does the equation Δh = v ΔP apply?
What is the relationship between specific heats for incompressible substances?
What is the relationship between specific heats for incompressible substances?
What approximate formula can be used for enthalpy changes in solids for small temperature intervals?
What approximate formula can be used for enthalpy changes in solids for small temperature intervals?
What is NOT a characteristic of incompressible substances during energy analysis?
What is NOT a characteristic of incompressible substances during energy analysis?
In analyzing specific heats of incompressible substances, what is the assumption for small temperature intervals?
In analyzing specific heats of incompressible substances, what is the assumption for small temperature intervals?
What is the correct expression for enthalpy change during a constant-pressure process involving liquids?
What is the correct expression for enthalpy change during a constant-pressure process involving liquids?
Flashcards
Moving Boundary Work (Wb)
Moving Boundary Work (Wb)
The work done by a system as its boundary (e.g., a piston) moves. It's the energy transferred across the system boundary due to changes in volume.
Quasi-Equilibrium Process
Quasi-Equilibrium Process
A process that occurs slowly enough that the system remains essentially in equilibrium at each instant.
Boundary Work in Constant-Volume Process
Boundary Work in Constant-Volume Process
Zero work is done because there's no change in volume.
Boundary Work in Constant-Pressure Process
Boundary Work in Constant-Pressure Process
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Boundary Work in Isothermal Process
Boundary Work in Isothermal Process
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Work at Inner Piston Face (Pi)
Work at Inner Piston Face (Pi)
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Energy Conservation
Energy Conservation
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Specific Heat at Constant Volume (cv)
Specific Heat at Constant Volume (cv)
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Specific Heat at Constant Pressure (cp)
Specific Heat at Constant Pressure (cp)
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Constant-Volume Process
Constant-Volume Process
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Constant-Pressure Process
Constant-Pressure Process
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Energy Conservation in Closed Systems
Energy Conservation in Closed Systems
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Property Relations
Property Relations
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Specific Heats Units
Specific Heats Units
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Ideal Gas Internal Energy
Ideal Gas Internal Energy
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Internal Energy - Real Gases
Internal Energy - Real Gases
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Internal Energy Dependence on Density
Internal Energy Dependence on Density
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Ideal Gas Enthalpy
Ideal Gas Enthalpy
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Ideal Gas Specific Heats
Ideal Gas Specific Heats
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Ideal-Gas Specific Heats
Ideal-Gas Specific Heats
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Ideal-gas Constant-Pressure Specific Heats
Ideal-gas Constant-Pressure Specific Heats
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Specific Heats Variation with Temperature
Specific Heats Variation with Temperature
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Internal Energy Change (Δu)
Internal Energy Change (Δu)
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Enthalpy Change (Δh)
Enthalpy Change (Δh)
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Reference Temperature
Reference Temperature
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Specific Heats
Specific Heats
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Ideal Gases
Ideal Gases
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cp and cv
cp and cv
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Specific Heat Ratio
Specific Heat Ratio
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Temperature Dependence
Temperature Dependence
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Monatomic Gases
Monatomic Gases
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Diatomic Gases
Diatomic Gases
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Hand Calculations
Hand Calculations
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Computerized Calculations
Computerized Calculations
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Average Specific Heats
Average Specific Heats
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Incompressible Substance
Incompressible Substance
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Specific Heats (c)
Specific Heats (c)
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Constant-Volume Specific Heat
Constant-Volume Specific Heat
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Constant-Pressure Specific Heat
Constant-Pressure Specific Heat
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Internal Energy Change (Δu)
Internal Energy Change (Δu)
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Enthalpy Change (Δh)
Enthalpy Change (Δh)
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Δh = Δu for Incompressible Solids/Liquids in Constant-Pressure Processes
Δh = Δu for Incompressible Solids/Liquids in Constant-Pressure Processes
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Δh = vΔP for Constant-Temperature Processes (Liquids)
Δh = vΔP for Constant-Temperature Processes (Liquids)
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Specific Heat (c) - Solids/Liquids
Specific Heat (c) - Solids/Liquids
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Constant-volume assumption
Constant-volume assumption
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Study Notes
Chapter 4: Energy Analysis of Closed Systems
- Thermodynamics textbook by Yunus A. Cengel and Michael A. Boles (5th/8th Ed., Chapters 4 and 5) is a recommended resource.
- Applied Thermodynamics by TD Eastop and A McConkey (5th Ed.) is also recommended.
- Moving boundary work (PdV work) is associated with expansion and compression in piston-cylinder devices.
- Exact determination of moving boundary work from thermodynamic analysis alone is not possible in real engines or compressors due to high piston speeds and variable gas equilibrium.
- Process paths are not always specified or possible to draw.
- Boundary work must be determined by direct measurements in real engines/compressors.
- Quasi-equilibrium processes are analyzed in this context.
- A quasi-equilibrium process involves nearly equilibrium conditions at all times.
- Differential work (δWb) during a quasi-equilibrium process is calculated using: δWb= F ds = Pa ds =P dV
- Total boundary work during a process is the sum of differential works from start to end, obtained by integration: Wb = ∫12PdV (kJ).
- Positive work signifies expansion, while negative work represents compression.
- Relationships between pressure (P) and volume (V) during expansion/compression are plotted on P-V diagrams.
- The area under the process curve on a P-V diagram is numerically equal to the boundary work done.
- Cyclic devices (e.g., car engines and power plants) will generate net work only if the work done during the cycle is not a path function.
- The net work done in a cycle is determined by calculating the difference in work done by and on the system.
- Pressure in the moving boundary work equation (P) is the pressure at the inner surface of the piston.
- The equation Wb=∫12 P dV (kJ) is valid for processes that are not quasi-equilibrium, provided the pressure at the inner face of piston is used instead of the instantaneous pressure inside the cylinder.
- Boundary work represents energy transferred into or out of a system during expansion or compression processes.
- Boundary work examples: in car engines, the work done by expanding hot gases moves the piston and crankshaft; or the work of moving boundary of the piston overcoming the frictional resistance between piston and cylinders, moving atmospheric air from the way and rotating the crankshaft
- The use of boundary work relation is not limited to quasi-equilibrium processes
- It is also applicable for solids and liquids, in addition to gases.
Constant-Volume Process (Isochoric)
- Boundary work (Wb) for a constant-volume process is zero because the volume change is null.
- Wb = ∫12 P dV = 0
Constant-Pressure Process (Isobaric)
- For this process: Wb = P(V2 - V1)
Isothermal Process
- For an isothermal process: Wb = mRT1 ln(V2/V1)
Polytropic Process
- Polytropic process relationship for gases: PVn = constant
- The total boundary work: Wb = (P2V2 - P1V1) / (1-n)
Specific Heats
- Specific heat is the energy required to raise the temperature of a unit mass of a substance by one degree.
- Specific Heat at constant volume (cv): energy required to raise the temperature of the unit mass of a substance by one degree with the volume maintained constant.
- Specific Heat at constant pressure (cp): energy required to raise the temperature of the unit mass of a substance by one degree with the pressure maintained constant.
- cp is always greater than cv .
Internal Energy and Enthalpy
- Internal energy is a function of temperature only for an ideal gas.
- Enthalpy is defined by h = u + Pv and is also dependent on temperature only for an ideal gas.
- Specific heats (cp and cv) are most often (but not always) dependent on temperature for real gas.
Ideal Gases
- Internal energy (u) and enthalpy (h) are functions of temperature only for ideal gases.
Incompressible Substances (Solids and Liquids)
- For incompressible substances, volume is constant.
- The specific heats cp and cv are identical and denoted by c.
- Internal energy change is du=c dT
- Enthalpy change is dh=c dT + v dP
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Description
Test your understanding of the energy analysis of closed systems in thermodynamics. This quiz covers topics such as moving boundary work, quasi-equilibrium processes, and the calculation of boundary work in real engines and compressors. Recommended resources include texts by Cengel, Boles, Eastop, and McConkey.
