1.4 Thermodynamic equilibrium and processes
3 min read•july 23, 2024
is the backbone of understanding system behavior. It's when a system's properties stay constant over time, with no energy or matter exchange. This state allows us to use key laws and principles to predict how systems will act.
Different types of processes, like isothermal and isobaric, show how systems change under various conditions. Quasi-static processes help us analyze systems that change slowly, while reversibility concepts explain ideal vs. real-world scenarios in thermodynamics.
Thermodynamic Equilibrium
Concept of thermodynamic equilibrium
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- Thermodynamic equilibrium refers to a state in which a system's macroscopic properties remain constant over time with no net exchange of energy or matter between the system and its surroundings
- Characterized by uniform temperature, pressure, and chemical potential throughout the system (thermal, mechanical, and )
- Allows for the application of thermodynamic laws and principles to calculate system properties and predict system behavior (ideal gas law, )
Types of thermodynamic processes
- occurs at constant temperature and requires heat exchange between the system and surroundings to maintain constant temperature, with work done by or on the system resulting in a change in (ideal gas expansion/compression)
- occurs at constant pressure and involves changes in volume and temperature, with and work occurring during the process (heating a gas at constant pressure)
- Isochoric (isovolumetric) process occurs at constant volume with no work done by or on the system, and heat transfer results in a change in internal energy and temperature (heating a gas in a sealed container)
- occurs without heat exchange between the system and surroundings, with work done by or on the system resulting in a change in temperature and internal energy, and rapid processes often approximating adiabatic conditions (compression stroke in an internal combustion engine)
Analysis of quasi-static processes
- occurs slowly enough for the system to remain infinitesimally close to equilibrium at all times, allowing for the application of equilibrium thermodynamic equations
- is a quasi-static process with no dissipative effects (friction, viscosity)
- Problem-solving approach for quasi-static processes:
- Identify the type of process (isothermal, isobaric, isochoric, or adiabatic)
- Apply the appropriate thermodynamic equations for the specific process:
- Ideal gas law:
- First law of thermodynamics:
- :
- Use given information to solve for unknown quantities
Reversibility vs irreversibility in thermodynamics
- Reversible process can be reversed without any net change in the system or surroundings, requires the process to be quasi-static and have no dissipative effects, and represents an ideal limit that actual processes can approach but never achieve ()
- cannot be reversed without a net change in the system or surroundings, involves dissipative effects (friction, viscosity, heat transfer across a finite temperature difference), and all real-world processes are irreversible to some extent
- Reversible processes establish the maximum theoretical efficiency for energy conversion devices (heat engines, refrigerators), while irreversibilities reduce the efficiency of real-world devices and processes
- The states that the of an isolated system always increases for irreversible processes
Key Terms to Review (19)
Adiabatic process: An adiabatic process is a thermodynamic process in which no heat is exchanged between the system and its surroundings. This means that any change in the internal energy of the system is entirely due to work done on or by the system, making it a critical concept in understanding various thermodynamic cycles and processes.
Carnot Cycle: The Carnot cycle is an idealized thermodynamic cycle that represents the most efficient way to convert heat into work, consisting of two isothermal and two adiabatic processes. This cycle serves as a benchmark for all real heat engines, highlighting the limits of efficiency based on the temperatures of the heat reservoirs involved.
Chemical Equilibrium: Chemical equilibrium is the state in which the concentrations of reactants and products in a chemical reaction remain constant over time, resulting in no net change. This balance occurs when the forward reaction rate equals the reverse reaction rate, leading to a dynamic but stable condition. Understanding chemical equilibrium involves recognizing how factors like temperature, pressure, and concentration can influence the position of equilibrium and the extent of a reaction.
Enthalpy: Enthalpy is a thermodynamic property that represents the total heat content of a system, defined as the sum of its internal energy and the product of its pressure and volume. This concept is crucial in understanding how energy is exchanged in processes, especially in the context of thermodynamic systems and the transformations they undergo.
Entropy: Entropy is a measure of the degree of disorder or randomness in a system, reflecting the number of microscopic configurations that correspond to a thermodynamic system's macroscopic state. It connects to various principles of thermodynamics, indicating how energy disperses and the direction of spontaneous processes.
First Law of Thermodynamics: The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This principle emphasizes the conservation of energy within a closed system, illustrating how energy transfers and transformations impact thermodynamic processes and systems.
Gibbs Free Energy: Gibbs free energy is a thermodynamic potential that measures the maximum reversible work obtainable from a closed system at constant temperature and pressure. It is a crucial concept because it helps predict the direction of chemical reactions and phase transitions, determining whether a process will occur spontaneously based on changes in enthalpy and entropy.
Heat Transfer: Heat transfer is the process of thermal energy moving from one object or system to another due to a temperature difference. This fundamental concept connects various phenomena, including how systems reach thermodynamic equilibrium and how energy is conserved in different processes.
Internal Energy: Internal energy is the total energy contained within a thermodynamic system, encompassing kinetic and potential energies of all the molecules in the system. This energy is crucial in determining the state of the system and plays a key role in thermodynamic processes, including heat transfer and work done on or by the system.
Irreversible process: An irreversible process is a type of thermodynamic process that cannot be reversed to restore the system and its surroundings to their original states without an increase in entropy. These processes often involve dissipative factors like friction, turbulence, or unrestrained expansion, which lead to a net change that cannot simply be undone. In understanding these processes, it's crucial to consider their role in defining thermodynamic equilibrium, how they differ from reversible processes, and their implications for concepts like entropy generation.
Isobaric Process: An isobaric process is a thermodynamic process that occurs at constant pressure. In such a process, any heat transfer into or out of the system results in a change in volume, while the pressure remains unchanged. This constancy of pressure plays a significant role in various energy exchanges and mechanical work done by or on the system.
Isothermal process: An isothermal process is a thermodynamic process in which the temperature of the system remains constant while heat is exchanged with the surroundings. This constant temperature implies that any internal energy changes in the system are fully compensated by heat transfer, making it an essential concept in understanding how systems behave under thermal equilibrium and the laws governing energy conservation.
Mechanical Equilibrium: Mechanical equilibrium refers to a state in which the sum of the forces acting on an object is zero, resulting in no net acceleration. In this state, an object remains at rest or continues to move with a constant velocity, indicating that all forces are balanced. Understanding mechanical equilibrium is crucial for analyzing thermodynamic processes, as it connects to the broader concept of thermodynamic equilibrium, where not only mechanical but also thermal and chemical aspects are balanced.
Quasi-static process: A quasi-static process is an idealized thermodynamic process that occurs infinitely slowly, allowing the system to remain in equilibrium at every intermediate state. This means that all variables, such as pressure and temperature, change gradually, ensuring that the system can be described as being in thermodynamic equilibrium throughout the process. This concept is crucial for distinguishing between reversible and irreversible processes, as it sets the stage for understanding how systems behave when they undergo slow changes.
Reversible Process: A reversible process is an idealized thermodynamic process that can be reversed without leaving any change in the system or its surroundings. In this type of process, both the system and the environment can return to their original states, making it an important concept for understanding efficiency and performance in thermodynamic cycles.
Second law of thermodynamics: The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and it dictates the direction of thermodynamic processes. This principle establishes that energy transformations are not 100% efficient, highlighting the inherent tendency for systems to move towards a state of greater disorder or randomness, affecting heat transfer, the performance of engines, and various processes in nature.
Thermal Equilibrium: Thermal equilibrium occurs when two or more bodies in thermal contact no longer exchange heat energy, resulting in them being at the same temperature. This state is crucial in understanding how energy transfers between systems and how those systems interact during various thermodynamic processes, influencing concepts such as heat capacity, statistical mechanics, and phase transitions.
Thermodynamic equilibrium: Thermodynamic equilibrium is the state in which a system's macroscopic properties are constant over time and there are no net flows of energy or matter within the system or between the system and its surroundings. In this state, the various forms of energy, such as thermal, mechanical, and chemical, are balanced, leading to uniform temperature and pressure throughout the system. Understanding this concept is crucial for analyzing state variables, processes, and the implications of laws like absolute zero and the Third Law of thermodynamics.
Work done by the system: Work done by the system refers to the energy transferred by a thermodynamic system as it performs work on its surroundings. This concept is vital in understanding how systems interact with their environment, particularly during processes where energy transformations occur, influencing the state of the system and its internal energy and enthalpy changes.