Thermodynamics of phase transitions akkamma

Thermodynamics of phase transitions akkamma

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  THERMODYNAMICS OF PHASE TRANSITIONS
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  Plan of talk 1)Definitionsof Phase Phase transition Phase Diagram 2)Types of phase transition • First order phase transition • Second order phase transition a) Sublimation line b) Melting line c) condensation line
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  Phase • Phase isdefined as a system which is homogeneous and has a definite boundary , it may be chemically pure substance or may contain more than one component as in the case of air or a mixture of two miscible liquids. Phase transition • It is a process in which a thermodynamic system undergoes changes from one state to another with different physical properties.
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  Phase Diagram For agiven set of independent variables,the phases that are realized in nature are those with the lowest free energy. The Gibbs free energy is a function of T,P& N. At constant temperature and pressure, Gibbs free energy is proportional to the number of particles, i.e. G(T,P, N)=Ng(T,P)
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  Phase transitions offirst and second order First order: 1) G(T, P) continuous; 2) and discontinuous; 3) Ǝ latent heat
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  Concept of phase P-Tdiagram for water
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  Second order 1) G(T,P) continuous; 2) S(T, P) and V(T, P) continuous; 3) response functions (susceptibilities) discontinuous:
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  Second order • Thefirst derivative of Gibb’s free energy are continuous but its second derivative shows discontinuous change as a substance passes from one phase to another. The three coexistence lines are: 1) Sublimation line 2) Melting line 3) condensation line
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  1)Sublimation line • Herethe solid coexists with the gas.
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  2) Melting line Itsalso called fusion line. Here the solid coexists with the liquid. Second order phase transitions are usually associated with the abrupt changes in the various properties characterizing the symmetry of a body.
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  3) Condensation line Itsalso called the vapour pressure line. Here the gas coexists with the liquid. The line begins at the triple point and ends at the critical point C.