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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 ...
Equilibrium chemistry is concerned with systems in chemical equilibrium.The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero.
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.
[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.
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:
The Hammett equation predicts the equilibrium constant or reaction rate of a reaction from a substituent constant and a reaction type constant. The Edwards equation relates the nucleophilic power to polarisability and basicity. The Marcus equation is an example of a quadratic free-energy relationship (QFER). [citation needed]
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]