Ehrenfest's equations

Ehrenfest's equations [′er·ən‚fests i‚kwā·zhənz]

(thermodynamics)

Equations which state that for the phase curveP(T) of a second-order phase transition the derivative of pressurePwith respect to temperatureTis equal to (C^f_p- Cⁱ_p)/TV(γ^f- γⁱ) = (γ^f- γⁱ)/(K^f-Kⁱ), whereiandfrefer to the two phases, γ is the coefficient of volume expansion,Kis the compressibility,C_pis the specific heat at constant pressure, andVis the volume.