I have just started learning thermodynamics. I have learned that The system which is not able to exchange energy and matter on its own with surrounding is called isolated system.

I wanted to know that practically is it possible to make 100% isolated system?

  • 3
    $\begingroup$ You could argue that the universe as a whole is such an isolated system. $\endgroup$
    – Philipp
    Commented Nov 7, 2014 at 10:08
  • $\begingroup$ @Philipp ah interesting! Please put that as answer. $\endgroup$
    – Freddy
    Commented Nov 7, 2014 at 10:39

3 Answers 3


There are no 100% isolated systems - even the universe itself may not be truly isolated (depending on how you define universe).

However, in practice, many systems are "isolated enough" that we can treat them as conserving mass and energy, especially over short time frames or small distances.

For example, we often treat a well-insulated and closed reaction vessel as isolated when doing thermodynamic calculations, and this approximation works very well for fast reactions.

Another example where this works is an adiabatic process. Many processes can be successfully modeled as adiabatic even though they happen in poorly-insulated containers - for example, the rapid expansion or compression of a gas.

Another example is the use of small sub-domains of a non-isolated system, which over short time scales behave as isolated systems themselves. For example, in finite element methods (FEM), a system is broken up into very small sub-domains. Each one acts as a small system in which mass and energy can transfer across the boundaries. Locally, an element is an open system, and over long time scales the entire system is open, but on short time scales, the sets of domains that share boundaries are treated as isolated. If energy leaves one domain, it enters the neighboring domain - it doesn't completely leave the system. In effect, you can model an open system as a large collection of isolated systems, with the outermost having open boundaries.

As you can see, even though the assumption of an isolated system is not really true, you can find many, many places where it is "true enough" that we can use it practically. In fact, it would be very hard to do anything in thermodynamics without it!


It is an idealized situation, an extreme, just as well all the other thermodynamic models.


An isolated system does not exchange energy or matter with its surroundings. For example, if soup is poured into an insulated container and closed, there is no exchange of heat or matter. The fact that, in reality, a thermos is not perfect in keeping things warm/cold illustrates the difficulty in creating an truly isolated system. In fact, there are a few, if any, systems that exist in this world that are completely isolated systems.

The universe of course is an another approximation of an isolated system.

So, practically it is impossible to make 100% isolated system.

  • 2
    $\begingroup$ "The universe of course is an another approximation of an isolated system." Do we know that? Has it been proven or are we just assuming here? $\endgroup$
    – tschoppi
    Commented Nov 7, 2014 at 14:15
  • $\begingroup$ We have conservation of energy in the universe (It's a physical principle). And we have the principle of the equivalence mass-energy . So, it's not an assumption. $\endgroup$ Commented Nov 7, 2014 at 14:27
  • $\begingroup$ So is the conservation of energy shown or simply postulated? We also have principles in quantum chemistry but some of those are simply postulates. $\endgroup$
    – tschoppi
    Commented Nov 7, 2014 at 15:16
  • $\begingroup$ Complete isolation also assumes constant volume. The Universe is expanding, ie. has no constant volume. $\endgroup$
    – Greg
    Commented Nov 7, 2014 at 15:33

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