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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).
[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.
where k f is the rate constant for the forward reaction and k b is the rate constant for the backward reaction and the square brackets, […], denote concentration. If only A is present at the beginning, time t = 0 , with a concentration [A] 0 , the sum of the two concentrations, [A] t and [B] t , at time t , will be equal to [A] 0 .
Equality of forward and backward reaction rates, however, is a necessary condition for chemical equilibrium, though it is not sufficient to explain why equilibrium occurs. Despite the limitations of this derivation, the equilibrium constant for a reaction is indeed a constant, independent of the activities of the various species involved ...
The second law of thermodynamics can be used to determine whether a hypothetical process is reversible or not. Intuitively, a process is reversible if there is no dissipation. For example, Joule expansion is irreversible because initially the system is not uniform. Initially, there is part of the system with gas in it, and part of the system ...
The equal sign refers to a reversible process, which is an imagined idealized theoretical limit, never actually occurring in physical reality, with essentially equal temperatures of system and surroundings. [10] [11] For an isentropic process, if also reversible, there is no transfer of energy as heat because the process is adiabatic; δQ = 0 ...
In physics, Loschmidt's paradox (named for J.J. Loschmidt), also known as the reversibility paradox, irreversibility paradox, or Umkehreinwand (from German 'reversal objection'), [1] is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics.
Classical thermodynamics deals with states of dynamic equilibrium.The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized (in the absence of an applied voltage), [2] or for which the entropy (S) is maximized, for specified conditions.