Podcast
Questions and Answers
What principle guides systems where experience is lacking or uncertain?
What principle guides systems where experience is lacking or uncertain?
What is typically the relationship between systems as they approach equilibrium?
What is typically the relationship between systems as they approach equilibrium?
Which of the following factors can prevent the realization of maximum work from systems?
Which of the following factors can prevent the realization of maximum work from systems?
How quickly do some systems, such as chemical reactions, reach equilibrium?
How quickly do some systems, such as chemical reactions, reach equilibrium?
Signup and view all the answers
What does the second law of thermodynamics help evaluate quantitatively?
What does the second law of thermodynamics help evaluate quantitatively?
Signup and view all the answers
What is a consequence of an imbalance between two systems?
What is a consequence of an imbalance between two systems?
Signup and view all the answers
Which aspect does the second law of thermodynamics NOT address?
Which aspect does the second law of thermodynamics NOT address?
Signup and view all the answers
What happens to the opportunity for work when systems move toward equilibrium uncontrolled?
What happens to the opportunity for work when systems move toward equilibrium uncontrolled?
Signup and view all the answers
What is required for reversing a process back to its initial condition in the examples provided?
What is required for reversing a process back to its initial condition in the examples provided?
Signup and view all the answers
In the context of energy conservation, what happens when a mass falls and comes to rest?
In the context of energy conservation, what happens when a mass falls and comes to rest?
Signup and view all the answers
Why is it stated that the inverse process does not take place spontaneously?
Why is it stated that the inverse process does not take place spontaneously?
Signup and view all the answers
Which of the following best describes what can typically enable the preferred direction of a process?
Which of the following best describes what can typically enable the preferred direction of a process?
Signup and view all the answers
What is necessary for air to flow back into the tank, according to the content?
What is necessary for air to flow back into the tank, according to the content?
Signup and view all the answers
What conclusion can generally be drawn about processes consistent with energy conservation?
What conclusion can generally be drawn about processes consistent with energy conservation?
Signup and view all the answers
When the mass reaches the temperature of its much larger surroundings, what happens to the internal energy?
When the mass reaches the temperature of its much larger surroundings, what happens to the internal energy?
Signup and view all the answers
What happens to the system’s conditions as auxiliary means function to restore the initial state?
What happens to the system’s conditions as auxiliary means function to restore the initial state?
Signup and view all the answers
What does the Clausius Statement of the Second Law of Thermodynamics suggest?
What does the Clausius Statement of the Second Law of Thermodynamics suggest?
Signup and view all the answers
Which statement is associated with the Kelvin-Planck formulation of the Second Law?
Which statement is associated with the Kelvin-Planck formulation of the Second Law?
Signup and view all the answers
In the context of thermodynamics, what distinguishes an extensive property like entropy?
In the context of thermodynamics, what distinguishes an extensive property like entropy?
Signup and view all the answers
Which of the following is considered a thermal reservoir?
Which of the following is considered a thermal reservoir?
Signup and view all the answers
Which formulation of the Second Law is primarily focused on the concept of entropy?
Which formulation of the Second Law is primarily focused on the concept of entropy?
Signup and view all the answers
What is the primary basis for the validity of the Second Law of Thermodynamics?
What is the primary basis for the validity of the Second Law of Thermodynamics?
Signup and view all the answers
How is temperature defined in relation to the Second Law of Thermodynamics?
How is temperature defined in relation to the Second Law of Thermodynamics?
Signup and view all the answers
How does the Second Law of Thermodynamics impact fields outside of engineering thermodynamics?
How does the Second Law of Thermodynamics impact fields outside of engineering thermodynamics?
Signup and view all the answers
What characterizes an internally reversible process?
What characterizes an internally reversible process?
Signup and view all the answers
In the example of water evaporating at 100 °C, what is considered an external irreversibility?
In the example of water evaporating at 100 °C, what is considered an external irreversibility?
Signup and view all the answers
According to the Kelvin-Planck statement, what must be true for a system undergoing a thermodynamic cycle?
According to the Kelvin-Planck statement, what must be true for a system undergoing a thermodynamic cycle?
Signup and view all the answers
What can be concluded regarding the thermal efficiency of a power cycle interacting with two thermal reservoirs?
What can be concluded regarding the thermal efficiency of a power cycle interacting with two thermal reservoirs?
Signup and view all the answers
Which of the following statements about the Carnot corollaries is true?
Which of the following statements about the Carnot corollaries is true?
Signup and view all the answers
What happens to the remaining heat during a cycle operating between two thermal reservoirs?
What happens to the remaining heat during a cycle operating between two thermal reservoirs?
Signup and view all the answers
Which of the following correctly illustrates the difference between internal and external irreversibilities?
Which of the following correctly illustrates the difference between internal and external irreversibilities?
Signup and view all the answers
What is a key implication of the first Carnot corollary?
What is a key implication of the first Carnot corollary?
Signup and view all the answers
What happens to the gas in a rigid tank when work flows into the system?
What happens to the gas in a rigid tank when work flows into the system?
Signup and view all the answers
In the first process described for the gas in a rigid tank, what is the direction of heat transfer?
In the first process described for the gas in a rigid tank, what is the direction of heat transfer?
Signup and view all the answers
Which of the following statements is true regarding the increase in internal energy of the surroundings?
Which of the following statements is true regarding the increase in internal energy of the surroundings?
Signup and view all the answers
What occurs when the interconnecting valve is opened in the closed tank of air at high pressure?
What occurs when the interconnecting valve is opened in the closed tank of air at high pressure?
Signup and view all the answers
What is the direction of work flow when extracting work from the gas system?
What is the direction of work flow when extracting work from the gas system?
Signup and view all the answers
Why would the inverse process of an object warming from a lower temperature not occur spontaneously?
Why would the inverse process of an object warming from a lower temperature not occur spontaneously?
Signup and view all the answers
What effect does raising a weight using the paddle in Process II have on the gas system?
What effect does raising a weight using the paddle in Process II have on the gas system?
Signup and view all the answers
Which process demonstrates heat being transferred to the gas system?
Which process demonstrates heat being transferred to the gas system?
Signup and view all the answers
What indicates the cycle is irreversible when comparing cycle performance?
What indicates the cycle is irreversible when comparing cycle performance?
Signup and view all the answers
Which statement correctly describes a Carnot cycle?
Which statement correctly describes a Carnot cycle?
Signup and view all the answers
How can a Carnot power cycle be adapted for refrigeration or heat pump operations?
How can a Carnot power cycle be adapted for refrigeration or heat pump operations?
Signup and view all the answers
What does the Clausius inequality facilitate in thermodynamics?
What does the Clausius inequality facilitate in thermodynamics?
Signup and view all the answers
In the context of cycle performance, what is represented by hmax?
In the context of cycle performance, what is represented by hmax?
Signup and view all the answers
What is the main feature of the processes in a Carnot cycle?
What is the main feature of the processes in a Carnot cycle?
Signup and view all the answers
What does the coefficient of performance measure in a Carnot refrigeration cycle?
What does the coefficient of performance measure in a Carnot refrigeration cycle?
Signup and view all the answers
What does comparing h and hmax determine about a cycle's performance?
What does comparing h and hmax determine about a cycle's performance?
Signup and view all the answers
Study Notes
Chapter 5: The Second Law of Thermodynamics
- The second law of thermodynamics dictates the direction of a thermodynamic process.
- The first law (conservation of mass and energy) does not dictate the direction.
- Only spontaneous processes are allowed.
- The second law provides a guiding principle to determine whether a process can occur thermodynamically
- Irreversible processes are those where the initial condition cannot be restored spontaneously, but require external means.
- Irreversible processes include heat transfer with a finite temperature difference, unrestrained expansion of gas/liquids, spontaneous chemical reaction, and mixing of matter.
Learning Outcomes
- Explain key concepts of the second law, other statements of the second law, internally reversible process, and the Kelvin temperature scale.
- List important irreversibilities (e.g., heat transfer via finite temperature differences, unrestrained expansion).
- Evaluate power cycles and refrigeration and heat pump cycles using corollaries of sections 5.6.2 and 5.7.2, alongside equations 5.9-5.11.
- Describe the Carnot cycle.
- Apply the Clausius inequality as expressed by Eq. 5.13.
Aspects of the Second Law of Thermodynamics
- Conservation of mass and energy principles indicate the disposition of mass and energy in a process, but do not tell us if the process is possible.
- The second law tells us which processes are thermodynamically feasible.
- The second law has various aspects: predicting process direction, establishing equilibrium conditions, determining the best theoretical performance of cycles, engines, and other devices, and quantitatively evaluating factors that preclude optimal performance.
Motivation
- The first law is a mathematical statement of energy conservation (Q – W = ΔU).
- The first law does not specify the direction of a process.
- Consider processes involving heat transfer between hot and cold bodies, the natural direction is from hot to cold.
Allowable Processes
- Process I (work done on system): work input, heat output from the system.
- Process II (heat transfer to system): heat input, work output from the system.
- Process I is spontaneous, II is not.
Aspects of the Second Law (cont.)
- The second law, unlike the first, establishes preferred directions for processes.
- Some processes are allowed while others are disallowed by the second law, even though they satisfy the first (conservation) law.
Kelvin-Planck Statement
- It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of work to its surroundings while receiving energy by heat transfer from a single thermal reservoir.
- Any engine cannot have 100% thermal efficiency.
- Thermal efficiency (η) must be less than 100%.
Entropy Statement
- Entropy is an extensive property.
- Entropy is unlike mass and energy, which are conserved. Entropy is produced whenever non-idealities are present.
- It is impossible for a system to operate in a way that destroys entropy.
Entropy Statement (mathematical interpretation)
- The change in entropy of a system within a time interval equals the net amount of entropy transferred across the system boundary during the time interval plus the net entropy produced by the system within the time interval.
- The entropy production is never negative. The process is possible only if the entropy production is positive or zero.
Irreversibilities
- Actual processes are different from idealized ones because of non-idealities, called irreversibilities.
- Common irreversibilities include heat transfer through finite temperature differences, unrestrained expansion, spontaneous chemical reaction, mixing of matter, friction, electric current flow through a resistance, magnetization/polarization with hysteresis, and inelastic deformation.
Irreversible and Reversible Processes
- A process is irreversible if irreversibilities are present within the system and/or its surroundings.
- All actual processes are irreversible.
- A process is reversible if no irreversibilities are present.
- An internally reversible process is a quasi-equilibrium process.
Example: Internally Reversible Process
- Water evaporating within a piston-cylinder: a sequence of equilibrium states exists during the phase change. The heat transfer to the water is an irreversibility in the surroundings (external).
Analytical Form of the Kelvin-Planck Statement
- For a system undergoing a thermodynamic cycle, the net work cannot be positive (Wcycle ≤ 0) if it communicates thermally with a single reservoir only.
Applications to Power Cycles Interacting with Two Thermal Reservoirs
- For a system undergoing a power cycle while communicating thermally with two thermal reservoirs the thermal efficiency is given by
η= Wcycle / QH = 1 – Qc / QH. (Eq. 5.4).
Carnot cycle
- The Carnot cycle provides a specific example of a reversible engine between two thermal reservoirs.
- The cycle involves two adiabatic and two isothermal processes.
Carnot Refrigeration Heat Pump Cycles
- If a Carnot power cycle is reversed, this is equivalent to a refrigeration or heat pump cycle with the same magnitudes of heat transfers but opposite directions.
- Coefficients of performance (COP) for such cycles are:
- Carnot refrigeration: βmax = Tc / (Th - Tc) (Eq. 5.10)
- Carnot heat pump: γmax = Th / (Th - Tc) (Eq. 5.11)
Clausius Inequality
- The Clausius inequality is applicable to any cycle, regardless of the body(ies) from which the system receives energy during a heat transfer.
- The mathematical form of Clausius Inequality is: ∮(δQ/T) ≤ 0
Example Use of Clausius Inequality
- The Clausius inequality can be used to determine if a cycle is reversible, irreversible, or impossible.
- Calculations involving heat transfer and temperatures are used.
Maximum Performance Measures for Cycles
- Thermal efficiency of an irreversible cycle is always less than the thermal efficiency of the reversible cycle.
- Coefficient of performance of an irreversible refrigeration/heat pump cycle is always less than the coefficient of performance of the reversible equivalent.
Kelvin Temperature Scale
- Defined using reversible cycles as their basis.
- The ratio of heat transfers is equal to the inverse ratio of the Kelvin temperatures of the hot and cold reservoirs
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your understanding of key concepts in thermodynamics, including the second law, equilibrium states, and energy conservation. This quiz will challenge your knowledge of how systems behave under various conditions and the factors that influence their functionality. Explore these fundamental principles and their implications in real-world scenarios.
