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Donnan equilibrium across a cell membrane (schematic). The Gibbs–Donnan effect (also known as the Donnan's effect, Donnan law, Donnan equilibrium, or Gibbs–Donnan equilibrium) is a name for the behaviour of charged particles near a semi-permeable membrane that sometimes fail to distribute evenly across the two sides of the membrane. [1]
The definition of the Gibbs function is = + where H is the enthalpy defined by: = +. Taking differentials of each definition to find dH and dG, then using the fundamental thermodynamic relation (always true for reversible or irreversible processes): = where S is the entropy, V is volume, (minus sign due to reversibility, in which dU = 0: work other than pressure-volume may be done and is equal ...
Ellingham diagram for several metals giving the free energy of formation of metal oxides and the corresponding oxygen partial pressure at equilibrium. Ellingham diagrams are a particular graphical form of the principle that the thermodynamic feasibility of a reaction depends on the sign of Δ G , the Gibbs free energy change, which is equal to ...
In 1884, Jacobus van 't Hoff proposed the Van 't Hoff equation describing the temperature dependence of the equilibrium constant for a reversible reaction: = where ΔU is the change in internal energy, K is the equilibrium constant of the reaction, R is the universal gas constant, and T is thermodynamic temperature.
Combining expressions for the Gibbs–Duhem equation in each phase and assuming systematic equilibrium (i.e. that the temperature and pressure is constant throughout the system), we recover the Gibbs' phase rule. One particularly useful expression arises when considering binary solutions. [7] At constant P and T it becomes:
[11] [12] This time scale becomes shorter as the temperature is raised. In every reaction, the first product formed is that which is most easily formed. Thus, every reaction a priori starts under kinetic control. [13] A necessary condition for thermodynamic control is reversibility or a mechanism permitting the equilibration between products.
If it is defined that a thermodynamic system is in thermal equilibrium with itself (i.e., thermal equilibrium is reflexive), then the zeroth law may be stated as follows: If a body C, be in thermal equilibrium with two other bodies, A and B, then A and B are in thermal equilibrium with one another. [8]
At equilibrium, the rate of transfer of CO 2 from the gas to the liquid phase is equal to the rate from liquid to gas. In this case, the equilibrium concentration of CO 2 in the liquid is given by Henry's law, which states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. [1]