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An isothermal process is a type of thermodynamic process in which the temperature T of a system remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and a change in the system occurs slowly enough to allow the system to be continuously adjusted to the temperature of the reservoir through heat exchange (see quasi-equilibrium).
The choice to define compressibility as the negative of the fraction makes compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume. The reciprocal of compressibility at fixed temperature is called the isothermal bulk modulus .
Isothermal : The process is at a constant temperature during that part of the cycle (=, =). Energy transfer is considered as heat removed from or work done by the system. Energy transfer is considered as heat removed from or work done by the system.
The change in the Helmholtz energy during a process is equal to the maximum amount of work that the system can perform in a thermodynamic process in which temperature is held constant. At constant temperature, the Helmholtz free energy is minimized at equilibrium.
In 1968, Anderson developed (∂T/∂P) v =(αK) −1 for the thermal gradient, [7] and its reciprocal correlate the thermal pressure and temperature in a constant volume heating process by (∂P/∂T) v =αK. [8] Note, thermal pressure is the pressure change in a constant volume heating process, and expressed by integration of αK.
For a process at constant temperature and pressure without non-PV work, this inequality transforms into <. Similarly, for a process at constant temperature and volume, <. Thus, a negative value of the change in free energy is a necessary condition for a process to be spontaneous; this is the most useful form of the second law of thermodynamics ...
It corresponds exactly to the definition of negentropy adopted in statistics and information theory. A similar physical quantity was introduced in 1869 by Massieu for the isothermal process [10] [11] [12] (both quantities differs just with a figure sign) and by then Planck for the isothermal-isobaric process. [13]
While the magnitude of work and heat are equal for an isothermal process, the signs are different. So for an isothermal expansion, work is done by the gas (system) on the surroundings and the sign is negative by definition, but heat is absorbed by the gas and the sign is positive.