Podcast
Questions and Answers
What does the First Law of Thermodynamics state regarding a system's internal energy?
What does the First Law of Thermodynamics state regarding a system's internal energy?
- It only considers heat transfer into the system.
- It relates the change in internal energy to heat supplied and work done on the system. (correct)
- It is independent of work done on the system.
- It states that energy cannot be created or destroyed.
In the equation dU = dQ + dW, which of the following statements is true?
In the equation dU = dQ + dW, which of the following statements is true?
- dU is considered a function of state. (correct)
- dQ must always be negative for work to be positive.
- dQ and dW are dependent on the system's initial state.
- dW is a function of heat transfer only.
Which limitation is associated with the First Law of Thermodynamics?
Which limitation is associated with the First Law of Thermodynamics?
- It assumes all types of energies are equal. (correct)
- It sets a maximum limit on heat transfer.
- It provides a specific direction for energy transfer.
- It does not take into account the conversion efficiency of work.
If a system experiences a loss of 45 J of heat and 450 J of work is done on it, what will be the change in internal energy?
If a system experiences a loss of 45 J of heat and 450 J of work is done on it, what will be the change in internal energy?
What does the First Law of Thermodynamics imply about energy exchange in a system?
What does the First Law of Thermodynamics imply about energy exchange in a system?
Which statement correctly describes a closed system?
Which statement correctly describes a closed system?
What is an example of a quasi-equilibrium process?
What is an example of a quasi-equilibrium process?
Which of the following is not a path function?
Which of the following is not a path function?
Match the process with its correct description: What matches Heat to work?
Match the process with its correct description: What matches Heat to work?
Which of the following is associated with irreversibilities?
Which of the following is associated with irreversibilities?
What does the first law of thermodynamics primarily assert?
What does the first law of thermodynamics primarily assert?
If a system’s volume is constant while heat is added, what happens to its internal energy?
If a system’s volume is constant while heat is added, what happens to its internal energy?
What is characteristic of an open system?
What is characteristic of an open system?
Flashcards
First Law of Thermodynamics
First Law of Thermodynamics
The change in a system's internal energy equals the heat added plus the work done on the system.
Internal Energy (dU)
Internal Energy (dU)
The total energy stored within a system. It's a function of state (depends only on current conditions).
Heat (Ä‘Q)
Heat (Ä‘Q)
Energy transferred between a system and its surroundings due to temperature difference. Not a state function.
Work (Ä‘W)
Work (Ä‘W)
Signup and view all the flashcards
Change in Internal Energy Equation
Change in Internal Energy Equation
Signup and view all the flashcards
Closed System
Closed System
Signup and view all the flashcards
Open System
Open System
Signup and view all the flashcards
Quasi-Equilibrium Process
Quasi-Equilibrium Process
Signup and view all the flashcards
Path Function
Path Function
Signup and view all the flashcards
Control Mass
Control Mass
Signup and view all the flashcards
Control Volume
Control Volume
Signup and view all the flashcards
Internal Energy
Internal Energy
Signup and view all the flashcards
Study Notes
First Law of Thermodynamics
- The first law of thermodynamics is a statement of the conservation of energy
- During interactions, energy can change forms, but the total energy remains constant.
- Energy cannot be created or destroyed.
- The first law asserts energy is a thermodynamic property.
Learning Goals
- Students will be able to recognize basic terminology in thermal engineering.
- Students will be able to understand the first law of thermodynamics.
System Definitions
- Closed system = control mass
- Open system = control volume
- Closed system = control mass, a system where the mass remains constant
- Open system = control volume, a system where mass can cross the boundary
Quasi-Equilibrium Process
- A quasi-equilibrium process is a very slow compression of air in a cylinder.
Path Function vs. State Function (Example)
- Not a path function: Thermal conductivity
- Examples of path functions: Heat, Work, ∫vdP
Matching Terms (List I to List II):
- Heat to work: Heat engine
- Heat to lift weight: Hot air balloon
- Heat to strain energy: Bimetallic strips
- Heat to electromagnetic energy: Thermal radiation
Another Matching Set
- Irreversibilities: Thermal equilibrium
- Mechanical work: Inexact differences
- Zeroth law: High grade energy
- Heat: Entropy
The First Law Equation
- ΔU = Uf - Ui = Q - W
- ΔU = Change in internal energy
- Uf = Final internal energy
- Ui = Initial internal energy
- Q = Heat
- W = Work
Sign Conventions (for Q and W)
- Positive Q: System gains heat
- Negative Q: System loses heat
- Positive W: Work done by the system.
- Negative W: Work done on the system
Closed System Executing Cycle
- Cyclic integral of work = cyclic integral of heat.
- ∫dW = ∫dQ.
Closed System Undergoing a Process
- Total energy entering the system – total energy leaving the system = change in total energy of system
- △KE + △PE + △U = Q − W
Energy Balance of a System
- The first law of thermodynamics (FLT) is a powerful tool for analyzing energy exchange between a system and its surroundings.
- dU = dQ + dW (change in internal energy = heat + work)
Limitations of the First Law
- The first law assumes all types of energies are equal.
- It does not specify the direction of heat transfer and work transfer.
- The first law sets no limit on how much work can be produced from supplied heat.
Total Energy Exchange
- The total energy a system exchanges with its surroundings in any process depends only on the initial and final states, not how the change occurred.
Example Problem (Constant Pressure)
- A gas loses 45 J of heat to its surroundings and has 450 J of work done onto it. Find the change in internal energy.
- ΔU = 495J
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
