<unk> s is conducted under a system-centered view of the universe.  All quantities, such as pressure or mechanical work, in an equation refer to the system unless labeled otherwise.<unk> s is basically concerned with the flow and balance of energy and matter in a<unk> . Three types of<unk> s are distinguished depending on the kinds of interaction and energy exchange taking place between the system and its surrounding environment:
Isolated systems are completely isolated in every way from their environment. They do not exchange heat, work or matter with their environment. An example of an isolated system would be an insulated rigid container, such as an insulated gas cylinder.
Closed systems are able to exchange energy (heat and work) but not matter with their environment. A greenhouse is an example of a closed system exchanging heat but not work with its environment. Whether a system exchanges heat, work or both is usually thought of as a property of its boundary.
Open systems: exchanging energy (heat and work) and matter with their environment. A boundary allowing matter exchange is called permeable. The ocean would be an example of an open system.
In reality, a system can never be absolutely isolated from its environment, because there is always at least some slight coupling, even if only via minimal gravitational attraction. In analyzing a system in steady-state, the energy into the system is equal to the energy leaving the system .
As an example, consider the system of hot liquid water and solid table salt in a sealed, insulated test tube held in a vacuum (the surroundings). The test tube constantly loses heat (in the form of black-body radiation), but the heat loss progresses very slowly. If there is another process going on in the test tube, for example the dissolution of the salt crystals, it will probably occur so quickly that any heat lost to the test tube during that time can be neglected.<unk> s does not measure time, but it does sometimes accept limitations on the timeframe of a process.)
Thermodynamic system
Microbiology template
Chapter checklist
Drug page template
Kick chart
Laboratory findings template
Classification template
Cartesian coordinate system