In thermodynamics, a system is the specific part of the universe that we choose to study, usually a quantity of matter or a region in space where energy exchanges take place. Everything outside the system is called the surroundings.
Key Points:
- The system + surroundings = universe (in thermodynamic context).
- A system is defined by boundaries (real or imaginary) that separate it from the surroundings.
- Across these boundaries, energy (heat or work) and sometimes matter can be exchanged.
Types of Systems:
- Open System
- Can exchange both matter and energy with surroundings.
- Example: Boiling water in an open pot (steam escapes, heat is transferred).
- Closed System
- Can exchange energy but not matter with surroundings.
- Example: A sealed container of gas (heat can pass through walls, but gas cannot escape).
- Isolated System
- Cannot exchange matter or energy with surroundings.
- Example: A thermos flask (ideally prevents both heat and matter exchange).
In short:
A system in thermodynamics is the portion of the universe we focus on, separated by boundaries, where energy and matter interactions are studied.