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Ehrenfest classification


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A classification of phase transitions in terms of their thermodynamic properties put forward by the Dutch physicist Paul Ehrenfest (1880–1933). A first-order phase transition is a phase transition in which the first derivative of the chemical potential is discontinuous. In a first-order phase transition there is a nonzero change in the value of the enthalpy, entropy, and volume at the transition temperature. Melting and boiling are examples of first-order phase transitions. In a second-order phase transition, the first derivative of the chemical potential is continuous but its second derivative is not continuous. In a second-order phase transition there is no jump in the value of the enthalpy, entropy, and volume at the transition temperature. Examples of second-order phase transitions include the transition to ferromagnetism and order-disorder transitions in alloys.

Subjects: Chemistry.


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