system

(noun)

the part of the universe being studied, arbitrarily defined to any size desired

Related Terms

Examples of system in the following topics:

  • Comparison of Enthalpy to Internal Energy

    • A thermodynamic system can be any physical system with a well-defined volume in space.
    • The outer edge of the system is referred to as its boundary, which often separates the system from the surroundings.
    • Hence, -q means the system loses heat, while +q means a system gains heat.
    • Similarly, +w means work is done on the system, while -w means work is done by the system.
    • However, in open systems, the pressure of the system and the surroundings has stayed constant.

  • Changes in Energy

    • For isolated systems, entropy never decreases.
    • Increases in entropy correspond to irreversible changes in a system.
    • This is because some energy is expended as heat, limiting the amount of work a system can do.
    • The state function has the important property that in any process where the system gives up energy ΔE, and its entropy falls by ΔS, a quantity at least TR ΔS of that energy must be given up to the system's surroundings as unusable heat (TR is the temperature of the system's external surroundings).
    • The entropy of a system is defined only if it is in thermodynamic equilibrium.

  • The Three Laws of Thermodynamics

    • Everything that is not a part of the system constitutes its surroundings.
    • The system and surroundings are separated by a boundary.
    • A closed system may still exchange energy with the surroundings unless the system is an isolated one, in which case neither matter nor energy can pass across the boundary.
    • Conversely, heat flow out of the system or work done by the system (on the surroundings) will be at the expense of the internal energy, and q and w will therefore be negative.
    • Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system.

  • Microstates and Entropy

    • Energy can be shared between microstates of a system.
    • With more available microstates, the entropy of a system increases.
    • These processes reduce the state of order of the initial systems.
    • With more available microstates, the entropy of a system increases.
    • The more such microstates, the greater is the probability of the system being in the corresponding macrostate.

  • Free Energy and Work

    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • Gibbs energy is the maximum useful work that a system can do on its surroundings when the process occurring within the system is reversible at constant temperature and pressure.
    • The work is done at the expense of the system's internal energy.
    • ΔG is the maximum amount of energy which can be "freed" from the system to perform useful work.
    • "Useful" in this case, refers to the work not associated with the expansion of the system.

  • The Third Law of Thermodynamics and Absolute Energy

    • The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches zero.
    • At zero temperature the system must be in a state with the minimum thermal energy.
    • A more general form of the third law applies to systems such as glasses that may have more than one minimum energy state: the entropy of a system approaches a constant value as the temperature approaches zero.
    • The constant value (not necessarily zero) is called the residual entropy of the system.
    • For such systems, the entropy at zero temperature is at least ln(2)kB, which is negligible on a macroscopic scale.

  • Pressure and Free Energy

    • Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure.
    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force.
    • Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature.

  • Standard Units (SI Units)

    • The International System of Units (abbreviated SI) is the metric system used in science, industry, and medicine.
    • The International System of Units (abbreviated SI, from the French Système international d'unités) is the metric system used in science, industry, and medicine.
    • The imperial system is used for "everyday" measurements in a few places, such as the United States.
    • The use of the SI system provides all scientists and engineers with a common language of measurement.
    • Causey teaches scientific units of the SI system, the metric system, and the CGS system.

  • Internal Energy and Enthalpy

    • In thermodynamics, work (W) is defined as the process of an energy transfer from one system to another.
    • The first law of thermodynamics states that the energy of a closed system is equal to the amount of heat supplied to the system minus the amount of work done by the system on its surroundings.
    • The amount of energy for a closed system is written as follows:
    • In this equation, U is the total energy of the system, Q is heat, and W is work.
    • By adding the PV term, it becomes possible to measure a change in energy within a chemical system, even when that system does work on its surroundings.

  • Copolymers

    • The following examples refer to a two component system, in which one monomer is designated A and the other B.