Isolated System vs Closed System
For the purpose of chemistry, the universe is divided into two parts. The part we are interested in is called a system and the rest is called the surrounding. A system can be an organism, a reaction vessel or even a single cell. There are boundaries between a system and the surrounding. The scope of the system is defined by these boundaries. Sometimes matters and energy can be exchanged through these boundaries. The systems are distinguished by the kind of interactions they have or by the types of exchanges take place. The systems can be classified into two as open systems and closed systems. In an open system, the matter and energy can be transferred through the boundary between the system and the surrounding.
If the matter cannot be transferred through the boundary, then that kind of system is called a closed system. However, in a closed system, energy can be exchanged with the surroundings. The matter inside a closed system is always the same. When a reaction happens, the system can expand, or it can transfer energy to the surrounding if it is at a lower temperature.
Isolated system is also a closed system. But it differs from a closed system because, isolated systems have neither mechanical nor thermal contact with its surrounding. With time, isolated systems reach thermodynamical equilibrium by balancing the pressure, temperature or other differences.
Practically, there aren’t any isolated systems, because all the things are interacting with one another in certain ways. However, whole universe can be considered as an isolated system considering there is no transferring of matter and energy outside the universe. Theoretically, this has been defined when constructing models. For example, the first and second thermodynamics laws are described for the isolated systems. The first law of thermodynamics states that the “internal energy of an isolated system is constant.” The second law of thermodynamics says that “the entropy of an isolated system increases in the course of a spontaneous process.” This law is only true for isolated systems. The entropy will increase over time in an isolated system, and will reach the maximum value at the equilibrium. In an isolated system, the overall energy can never increase, thus the entropy can never decrease.
What is the difference between Isolated System and Closed System?
- In a closed system, matter cannot be exchanged with the surrounding, however energy can be exchanged. But in an isolated system, both matter and energy cannot be exchanged with the surrounding. Therefore, isolated system is more restricted than a closed system.
- Isolated systems are theoretical, whereas closed systems can really exist. For example, a closed system is where fluid is compressed in a piston. There the mass of the fluid doesn’t change, but the volume may change.
- The entropy of a closed system can be decreased, but in an isolated system, the entropy can never decrease.
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