Questions and Answers
What is a system in thermodynamics?
A system is defined as a quantity of matter or a region in space chosen for a particular study.
What is defined as the surroundings of a system?
The mass or region outside the system.
What separates the system from its surroundings?
The boundary.
Which type of system has a fixed amount of mass and no mass can cross its boundary?
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Which type of system allows both mass and energy to cross its boundary?
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What is an isolated system?
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Which of the following properties is intensive?
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What does the concept of continuum assume?
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What must occur for a system to be in an equilibrium state?
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Which of the following is NOT a type of process in thermodynamics?
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What defines a cycle in thermodynamics?
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What is the steady-flow process?
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In thermodynamics, work and heat are both state functions.
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Study Notes
System and Surroundings
- A system is a defined quantity of matter or a region in space selected for study.
- Surroundings refer to everything outside the system.
- A boundary separates the system from its surroundings; it can be fixed, movable, and has no thickness.
Types of Systems
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Closed Systems
- Known as control mass; contains a fixed amount of mass.
- Mass cannot cross the boundary, but energy (heat or work) can.
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Open Systems
- Also known as control volume; both mass and energy can cross boundaries.
- Common in devices involving mass flow like compressors and turbines.
- Control surface can be real or imaginary, and may vary in size and shape.
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Isolated Systems
- A special type of closed system where neither energy nor matter can be exchanged with surroundings.
Properties of a System
- Properties include pressure (P), temperature (T), volume (V), and mass (m), among others.
- Properties can be categorized as:
- Intensive properties: Independent of mass (e.g., temperature, pressure).
- Extensive properties: Dependent on size or extent (e.g., total mass, total volume).
- Specific properties: Extensive properties per unit mass (e.g., specific volume, specific total energy).
Continuum Concept
- The continuum assumption treats matter as continuous and homogeneous, ignoring molecular structure.
- Applicable when the system size is large compared to molecular spacing.
State and Equilibrium
- A state is defined by a set of properties that describe a system's condition; changes in one property alter the state.
- An equilibrium state refers to no unbalanced potentials within the system.
- Types of equilibrium include thermal, mechanical, phase, and chemical.
The State Postulate
- A simple compressible system’s state is identified by two independent intensive properties.
- For single-phase systems, temperature and specific volume can determine the state, while for multiphase systems, they may be dependent.
Processes and Cycles
- A process is a transition from one equilibrium state to another, with a sequence of states representing its path.
- Types of thermodynamic processes include:
- Adiabatic: No heat transfer.
- Isothermal: Constant temperature.
- Isobaric: Constant pressure.
- Isochoric: Constant volume.
- Isentropic: Constant entropy.
- Isenthalpic: Constant enthalpy.
Steady-Flow Process
- In a steady-flow process, fluid properties can vary from point to point within the control volume but remain constant at any fixed point.
- Ideal for continuous operation devices like turbines and pumps, while some cyclic devices can still be analyzed under steady-flow conditions with averaged properties.
Modes of Energy Transfer
- Heat: Energy transferred due to temperature differences.
- Work: Energy transferred through interactions other than heat.
- Both heat and work are recognized only during boundary crossing, are path-dependent, and represent energy interaction during processes rather than states.
Heat Transfer Modes
- Different methods of heat transfer include:
- Conduction
- Convection
- Radiation
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Description
This quiz covers the fundamental concepts of thermodynamics, focusing on the definitions of systems, surroundings, and boundaries. It is designed for students in the Earth Resources Engineering course at Moratuwa University. Test your understanding of these essential principles.
