System
Any part of the universe which is under study is called a system. It can be as simple as a gas contained in a closed vessel or as complicated as a rocket shooting towards moon. A system may be homogeneous or heterogeneous depending on its contents and conditions. A system is homogeneous if physical properties and chemical composition are identical throughout the system. Such a system is also called a single phase system A heterogeneous system consists of two or more than two phases separated by mechanical boundaries.
Surroundings
The rest of the universe around the system is considered its surroundings. A system and its surroundings are always separated by boundaries across which matter and energy may be exchanged. The boundaries can be real (fixed or moveable) or imaginary. Based on the exchange of matter and energy between the system and the surroundings, a system can be classified into the following three types:
(i) Isolated system
Isolated system is one which exchanges neither energy nor matter with its surroundings. There is no perfectly isolated system; but, a system which is thermally well insulated (i.e., does not allow heat flow) and is sealed to inflow or outflow of matter can be considered as an isolated system. A sealed thermos flask having-some matter thus approximates to art isolated system.
(ii) Closed system
Closed system allows exchange of energy (heat or work) with the surroundings but, matter is not allowed to enter or leave it. A properly scaled system (to prevent the passage of matter across its boundary) can be considered as a closed system.
(iii)Open system
Open system allows exchange of both matter and energy with its surroundings. This the most common type oil system encountered in our daily life. All living things are examples of open system since these are capable of freely exchanging energy and matter with their surroundings. Reaction vessels with permeable membranes are examples of open system.
reference
Advanced Chemistry (Physical and Industrial) Philip Mathews Cambridge University Press 2003 Physical Chemistry PW Atkins 3rd Edition Oxford University Press 1986
Be the first to comment