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In thermodynamics, the phase rule is a general principle governing multi-component, multi-phase systems in thermodynamic equilibrium.For a system without chemical reactions, it relates the number of freely varying intensive properties (F) to the number of components (C), the number of phases (P), and number of ways of performing work on the system (N): [1] [2] [3]: 123–125
Phase transitions and critical exponents appear in many physical systems such as water at the critical point, in magnetic systems, in superconductivity, in percolation and in turbulent fluids. The critical dimension above which mean field exponents are valid varies with the systems and can even be infinite.
As we approach the critical point, these diverging observables behave as () for some exponent , where, typically, the value of the exponent α is the same above and below T c. These exponents are called critical exponents and are robust observables. Even more, they take the same values for very different physical systems.
where α is an exponent specific to the system (e.g. in the absence of a potential field, α = 3/2), z is exp(μ/k B T) where μ is the chemical potential, Li is the polylogarithm, ζ is the Riemann zeta function, and T c is the critical temperature at which a Bose–Einstein condensate begins to form.
The discontinuity in , and other properties, e.g. internal energy, , and entropy,, of the substance, is called a first order phase transition. [12] [13] In order to specify the unique experimentally observed pressure, (), at which it occurs another thermodynamic condition is required, for from Fig.1 it could clearly occur for any pressure in the range .
The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken. [2] [3] Hess's law is now understood as an expression of the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state (i.e. enthalpy is a state ...
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter : solid , liquid , and gas , and in rare cases, plasma .
A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. [1]+ + 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.