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[a] While processes in isolated systems are never reversible, [3] cyclical processes can be reversible or irreversible. [4] Reversible processes are hypothetical or idealized but central to the second law of thermodynamics. [3] Melting or freezing of ice in water is an example of a realistic process that is nearly reversible.
Reversible process (thermodynamics), a process or cycle such that the net change at each stage in the combined entropy of the system and its surroundings is zero; Reversible reaction, a chemical reaction for which the position of the chemical equilibrium is very sensitive to the imposed physical conditions; so the reaction can be made to run ...
where a reversible path is chosen from absolute zero to the final state, so that for an isothermal reversible process Δ S = Q r e v T {\displaystyle \Delta S={Q_{rev} \over T}} . In general, for any cyclic process the state points can be connected by reversible paths, so that
For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings. Temperature is the thermodynamic conjugate variable to entropy, thus the conjugate process would be an isothermal process , in which the system is thermally "connected" to a constant-temperature heat bath.
For reversible (ideal) processes, the area under the T–s curve of a process is the heat transferred to the system during that process. [1] Working fluids are often categorized on the basis of the shape of their T–s diagram. An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal ...
Cyclic processes were important conceptual devices in the early days of thermodynamical investigation, while the concept of the thermodynamic state variable was being developed. (3) Defined by flows through a system, a flow process is a steady state of flows into and out of a vessel with definite wall properties. The internal state of the ...
First, it states that the microscopic detailed dynamics of particles and fields is time-reversible because the microscopic equations of motion are symmetric with respect to inversion in time ; Second, it relates to the statistical description of the kinetics of macroscopic or mesoscopic systems as an ensemble of elementary processes: collisions ...
A and B can react to form C and D or, in the reverse reaction, C and D can react to form A and B. This is distinct from a reversible process in thermodynamics. Weak acids and bases undergo reversible reactions. For example, carbonic acid: H 2 CO 3 (l) + H 2 O (l) ⇌ HCO 3 − (aq) + H 3 O + (aq).