Thermodynamic system
In thermodynamics, a thermodynamic system is anything whose thermodynamic properties are being studied.[1] Everything around the system is called its surroundings or environment. The system can exchange heat with its surroundings and do work on them through a boundary, which is an imagined wall that separates the system from the environment.[2]
Example
A car engine gives a simple example. If the engine is being studied, the burning petrol inside the cylinder is the thermodynamic system. The piston, exhaust system, radiator and the air outside make up the surroundings, and the boundary is the inner surface of the cylinder and piston.[3] A chemistry textbook describes the same kind of case: the substances taking part in the reaction are the system, and the engine and the rest of the universe are the surroundings.[4]
Exchange of energy
Energy can move into a system in two ways: the system can take in heat from its surroundings, or the surroundings can do work on the system.[5] For example, a metal wire at room temperature gains energy if it is put into hot water, or if it is bent quickly back and forth. Both make the wire warmer.[6]
Open and isolated systems
Normally a system interacts with its surroundings in some way.[7] Most systems are open systems, which can exchange energy, matter or both with their surroundings.[8] A system that is completely separated from its environment is called isolated and closed. An example is a gas surrounded by walls that cannot move and that do not let heat through.[9] In reality, such a system does not exist unless the whole universe is treated as the system. Otherwise it is used as a model for a real system that has very little interaction with its environment.[10]
Equilibrium
In thermodynamics, equilibrium is described as the state that an isolated system settles into when it is left to itself.[11] The zeroth law of thermodynamics says that if one object is in thermal equilibrium with two others, then those two must also be in thermal equilibrium with each other.[12]
Related pages
References
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
A thermodynamic system includes anything whose thermodynamic properties are of interest.
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
It is embedded in its surroundings or environment ; it can exchange heat with, and do work on, its environment through a boundary , which is the imagined wall that separates the system and the environment
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
For example, if we are studying a car engine, the burning gasoline inside the cylinder of the engine is the thermodynamic system; the piston, exhaust system, radiator, and air outside form the surroundings of the system. The boundary then consists of the inner surfaces of the cylinder and piston.
- ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "5.3 Enthalpy". Chemistry 2e. OpenStax. Retrieved 18 October 2026.
The substances involved in the reaction are the system, and the engine and the rest of the universe are the surroundings.
- ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "5.3 Enthalpy". Chemistry 2e. OpenStax. Retrieved 18 October 2026.
Energy is transferred into a system when it absorbs heat ( q ) from the surroundings or when the surroundings do work ( w ) on the system.
- ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "5.3 Enthalpy". Chemistry 2e. OpenStax. Retrieved 18 October 2026.
For example, energy is transferred into room-temperature metal wire if it is immersed in hot water (the wire absorbs heat from the water), or if you rapidly bend the wire back and forth (the wire becomes warmer because of the work done on it).
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
Normally, a system must have some interactions with its surroundings.
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
Most systems are known as an open system , which can exchange energy and/or matter with its surroundings
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
A system is called an isolated and closed system if it is completely separated from its environment—for example, a gas that is surrounded by immovable and thermally insulating walls.
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
In reality, a closed system does not exist unless the entire universe is treated as the system, or it is used as a model for an actual system that has minimal interactions with its environment.
- ↑ "Philosophy of Statistical Mechanics". Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 18 October 2026.
where equilibrium is defined as the state to which an isolated system converges when left to itself (Werndl & Frigg 2015b)
- ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "3.1 Thermodynamic Systems". University Physics Volume 2. OpenStax. Retrieved 18 October 2026.
The governing principle here is the zeroth law of thermodynamics , as described in Temperature and Heat on temperature and heat: If object 1 is in thermal equilibrium with objects 2 and 3, respectively, then objects 2 and 3 must also be in thermal equilibrium.