1.17.3: Iso-Variables

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Page ID: 394358

Michael J Blandamer & Joao Carlos R Reis
University of Leicester & Faculdade de Ciencias

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Isobaric: A given system is held at constant pressure.

Isothermal: A given system is held at constant temperature.

Isochoric: A given closed system is held at constant volume.

Isentropic: This condition, linked to the adiabatic constraint, requires that during a reversible change the entropy of a system remains constant in a particular thermodynamic process; e.g. compression. Adiabatic + Reversible = Isentropic. We can find isentropic processes which are irreversible. In this case they are not adiabatic.

Isolated System: The boundary insulates a given system from the surroundings . This is not really an iso-variable in the thermodynamic sense.

Isoperibol: In the vast majority of calorimetric experiments, the surroundings and the reaction vessel (the system+ container) are at constant temperature. When the experiment is initiated the composition of the closed system changes resulting from, for example, chemical reaction, mixing of liquids….. The temperature of the closed system changes albeit by a small amount because the processes taking place in the calorimeter are either exo- or endo-thermic. A sensitive detector is used to measure the change in temperature of the system. In pedantic terms the system is not constrained to be ‘isothermal’. So the calorimeter being used in such an experiment is an isoperibol calorimeter.