3.1 Thermodynamic Systems
3 min read•june 24, 2024
Thermodynamic systems are the foundation of understanding energy transfer and transformation. These systems, defined by boundaries, interact with their through heat and , leading to changes in like pressure, volume, and temperature.
Thermodynamic processes describe how systems evolve and interact with their . The laws of thermodynamics govern these processes, establishing principles of energy conservation and the direction of spontaneous changes, while concepts like help explain the natural world's behavior.
Thermodynamic Systems
Components of thermodynamic systems
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- Specific portion of the universe under study can be any size or shape (gas in a container, cup of coffee, living organism)
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- Interface that separates the system from its surroundings can be real or imaginary, fixed or movable
- Determines the type of system: open allows matter and energy exchange, closed allows only energy exchange, isolated allows neither matter nor energy exchange
- Surroundings
- Everything outside the system can interact with the system through the boundary (room where a gas container is located, air around a cup of coffee)
Thermal equilibrium and temperature
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- State in which two or more systems have the same temperature occurs when there is no net heat transfer between the systems
- Necessary condition for measuring temperature
- Zeroth Law of Thermodynamics
- If two systems are in with a third system, they are in thermal with each other allows for the definition of temperature
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- Measure of the average kinetic energy of the particles in a system directly related to the of the system
- Measured in Kelvin (K) or Rankine (°R) with 0 K representing absolute zero, the lowest possible temperature
Equations of state in thermodynamics
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- Mathematical relationship between the state variables of a system describes the thermodynamic state of a system (ideal gas law, van der Waals equation)
- State variables
- Macroscopic properties that describe the state of a system (pressure (P), volume (V), temperature (T), (U), entropy (S))
- Ideal gas law
- Equation of state for ideal gases relates pressure, volume, temperature, and the number of moles of gas
- , where is the number of moles and is the universal gas constant applies to gases at low pressures and high temperatures
Thermodynamic Processes
System-surroundings interactions in processes
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- Change in the state of a system due to energy transfer or can be reversible (system can return to its initial state) or irreversible (system cannot return to its initial state)
- Examples:
- : constant temperature
- : constant pressure
- : constant volume
- : no heat transfer
- Heat transfer ()
- Energy transfer due to a temperature difference between the system and its surroundings positive when energy flows into the system, negative when energy flows out of the system
- Work ()
- Energy transfer due to a force acting through a distance positive when work is done by the system on its surroundings, negative when work is done on the system
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- Change in internal energy () of a system is equal to the sum of heat transfer () and work () done on the system
- establishes the conservation of energy principle in thermodynamics
- Applied to various processes (isothermal, isobaric, isochoric, adiabatic) to determine changes in state variables and energy transfers
Advanced Thermodynamic Concepts
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- States that the total entropy of an isolated system always increases over time
- Introduces the concept of irreversibility in natural processes
- Entropy
- Measure of the disorder or randomness in a system
- Helps explain the direction of spontaneous processes
- Heat engines
- Devices that convert thermal energy into mechanical work (e.g., steam engines, internal combustion engines)
- Efficiency is limited by the Second Law of Thermodynamics
- Carnot cycle
- Theoretical thermodynamic cycle that describes the most efficient possible heat engine
- Consists of two isothermal and two adiabatic processes
Key Terms to Review (33)
Adiabatic process: An adiabatic process is a thermodynamic process in which no heat is exchanged with the surroundings. In such processes, changes in internal energy are solely due to work done by or on the system.
Adiabatic Process: An adiabatic process is a thermodynamic process in which no heat is transferred to or from the system. In other words, the system is thermally isolated from its surroundings, and any changes in the system's internal energy are due solely to work done on or by the system.
Boundary: A boundary is a real or imaginary surface that separates a thermodynamic system from its surroundings. It defines the limits within which the system's properties are analyzed.
Clausius statement of the second law of thermodynamics: The Clausius statement of the second law of thermodynamics asserts that it is impossible for a self-acting machine, unaided by any external force, to transfer heat from a cooler body to a hotter one. This principle underlines the unidirectional nature of spontaneous heat transfer.
Closed system: A closed system is a thermodynamic system in which matter cannot enter or leave, but energy can be exchanged with its surroundings. It is an idealized concept used to simplify the analysis of energy transfer processes.
Entropy: Entropy is a measure of the disorder or randomness in a system. It quantifies the number of possible microscopic configurations that correspond to a thermodynamic system's macroscopic state.
Environment: The environment in thermodynamics is everything outside the system being studied. It interacts with the system through exchanges of energy and matter.
Equation of state: An equation of state is a mathematical equation that describes the relationship between state variables such as pressure, volume, and temperature in a thermodynamic system. It is used to predict the state of a system under different conditions.
Equilibrium: Equilibrium is the state of a thermodynamic system where all macroscopic flows are balanced and properties do not change over time. In this state, the system’s temperature, pressure, and chemical potential are uniform throughout.
Extensive variable: An extensive variable is a property of a thermodynamic system that changes with the size or extent of the system, such as mass, volume, or total energy. Extensive variables are additive for subsystems.
First law of thermodynamics: The First Law of Thermodynamics states that energy cannot be created or destroyed in an isolated system, only transformed from one form to another. It is also known as the law of energy conservation.
First Law of Thermodynamics: The First Law of Thermodynamics states that energy can be transformed from one form to another, but it cannot be created or destroyed. It establishes the fundamental principle of energy conservation, which is crucial for understanding heat transfer, thermodynamic systems, and adiabatic processes in an ideal gas.
Intensive variable: An intensive variable is a physical quantity whose value does not depend on the size or extent of the system. Examples include temperature, pressure, and density.
Internal energy: Internal energy is the total energy contained within a system due to both the random motions of its particles and the potential energies of their interactions. It encompasses kinetic and potential energy at the microscopic level.
Internal Energy: Internal energy is the total energy contained within a thermodynamic system, consisting of the kinetic energy of the system's particles and the potential energy associated with the configuration of the particles. It is a fundamental concept in thermodynamics that describes the energy stored within a system, which can be altered through the processes of work and heat transfer.
Isobaric process: An isobaric process is a thermodynamic process in which the pressure remains constant. The work done by or on the system can be calculated using the formula $W = P \Delta V$, where $P$ is the constant pressure and $\Delta V$ is the change in volume.
Isobaric Process: An isobaric process is a thermodynamic process in which the pressure of a system remains constant throughout the process. This means that the system undergoes changes in volume, temperature, and other properties, but the pressure remains the same.
Isochoric process: An isochoric process is a thermodynamic process in which the volume remains constant. Since the volume does not change, no work is done by or on the system during this process.
Isochoric Process: An isochoric process, also known as an isovolumetric process, is a thermodynamic process in which the volume of a system remains constant while other variables, such as pressure and temperature, may change. This type of process is an important concept in the study of thermodynamic systems, thermodynamic processes, and the heat capacities of an ideal gas.
Isothermal Process: An isothermal process is a thermodynamic transformation that occurs at a constant temperature, during which the internal energy of an ideal gas remains unchanged. This process connects to concepts like heat transfer, work done on or by the system, and the laws governing energy conservation and entropy, emphasizing how energy flows and transforms while maintaining thermal equilibrium.
Open system: An open system is a thermodynamic system that can exchange both energy and matter with its surroundings. Unlike closed systems, open systems are not isolated and can interact with external environments.
Second Law of Thermodynamics: The Second Law of Thermodynamics is a fundamental principle that describes the natural tendency of energy to dissipate and become less useful over time. It establishes the directional nature of various processes and the limits on the efficiency of energy conversion within a system.
State Variables: State variables are the minimum set of variables needed to completely describe the condition or state of a thermodynamic system at a given point in time. These variables are used to define the system's thermodynamic state and how it changes during various processes.
Surroundings: Surroundings are everything external to the thermodynamic system being studied. They interact with the system by exchanging energy or matter.
System Boundary: The system boundary is a conceptual or physical interface that separates a thermodynamic system from its surroundings. It defines the region of interest and determines what is considered part of the system and what is considered the environment or surroundings.
Thermal equilibrium: Thermal equilibrium is the state in which two or more objects in thermal contact no longer exchange heat, resulting in a uniform temperature throughout the system. This occurs when the temperatures of the objects are equal.
Thermal Equilibrium: Thermal equilibrium is a state in which two or more objects or systems have reached the same temperature and no longer exchange heat energy. This concept is fundamental to understanding temperature, thermometers, heat transfer, and the behavior of thermodynamic systems.
Thermodynamic Process: A thermodynamic process refers to the changes in the state of a thermodynamic system as it evolves from an initial state to a final state. This process involves the exchange of energy, typically in the form of heat or work, between the system and its surroundings, and is governed by the laws of thermodynamics.
Thermodynamic system: A thermodynamic system is a specific portion of matter or a region in space chosen for analysis, where energy exchanges with its surroundings are studied. It can be isolated, closed, or open depending on the nature of the exchange.
Thermodynamic System: A thermodynamic system is a defined region in space that is the subject of a thermodynamic analysis. It is a collection of matter and energy that can exchange energy and matter with its surroundings, and its behavior is governed by the laws of thermodynamics.
Thermodynamic Temperature: Thermodynamic temperature is a fundamental concept in thermodynamics that quantifies the thermal state of a system. It is a measure of the average kinetic energy of the particles within a system and is used to describe the direction of heat transfer between systems.
Work: Work is the energy transferred to or from an object via a force acting upon it over a displacement. In physics, work is mathematically expressed as $W = F \cdot d \cdot \cos(\theta)$, where $F$ is the force, $d$ is the displacement, and $\theta$ is the angle between them.
Work: Work is a fundamental concept in physics that describes the transfer of energy due to the application of a force over a distance. It is a measure of the energy expended or transferred during a physical process and is a crucial factor in understanding the behavior of thermodynamic systems, electric potential, and the storage of energy in capacitors.