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The presence of reactants in an open beaker is an example of an open system. Here the boundary is an imaginary surface enclosing the beaker and reactants. It is named closed , if borders are impenetrable for substance, but allow transit of energy in the form of heat, and isolated , if there is no exchange of heat and substances.
An open system is also known as a flow system. The concept of an open system was formalized within a framework that enabled one to interrelate the theory of the organism, thermodynamics, and evolutionary theory. [1] This concept was expanded upon with the advent of information theory and subsequently systems theory. Today the concept has its ...
It is an acceptable idealization used in constructing mathematical models of certain natural phenomena; e.g., the planets in the Solar System, and the proton and electron in a hydrogen atom are often treated as isolated systems. But, from time to time, a hydrogen atom will interact with electromagnetic radiation and go to an excited state.
The construction of physical models is often a creative act, and many bespoke examples have been carefully created in the workshops of science departments. There is a very wide range of approaches to physical modeling, including ball-and-stick models available for purchase commercially, to molecular models created using 3D printers .
For a simple system, with only one type of particle (atom or molecule), a closed system amounts to a constant number of particles. However, for systems which are undergoing a chemical reaction, there may be all sorts of molecules being generated and destroyed by the reaction process. In this case, the fact that the system is closed is expressed ...
Although the reduction in the number of variables is a useful simplification, the main advantage comes from the fact that the Helmholtz free energy is minimized at equilibrium with respect to any unconstrained internal variables for a closed system at constant temperature and volume. This follows directly from the principle of minimum energy ...
One such potential is the Helmholtz free energy (A), for a closed system at constant volume and temperature (controlled by a heat bath): A = U − T S {\displaystyle A=U-TS} Another potential, the Gibbs free energy ( G ), is minimized at thermodynamic equilibrium in a closed system at constant temperature and pressure, both controlled by the ...
The terms closed system and open system have long been defined in the widely (and long before any sort of amplifier was invented) established subject of thermodynamics, in terms that have nothing to do with the concepts of feedback and feedforward. The terms 'feedforward' and 'feedback' arose first in the 1920s in the theory of amplifier design ...