OIA1011 PHASE EQUILIBRIUM

Definition of Gibbs Free Energy.

ΔG=ΔH−TΔS, where ΔG determines reaction spontaneity, but does not indicate rate of reaction.

Explain Gibbs Free Energy, ΔG.

ΔG = 0, equilibrium

ΔG <0, spontaneous

ΔG = -ve, exergonic

ΔG = +ve, endergonic

Phase Transition

Change in phase without altering chemical composition (e.g., ice melting).

Transition Temperature

The temperature at which two phases are in equilibrium & ΔG =0, e.g., H2O(s)↔H2O(l) at 0°C.

Phase Diagram

A map showing conditions at which various phases of substance are thermodynamically stable.

Define a phase.

A homogenous, physically distinct portion of system which is separated from each other portions of system by bounding surfaces.

Critical Point

End point of pressure-temperature curve that designate conditions where liquid & it’s vapour can coexist.

At higher temperatures, gas cannot liquefied by pressure alone.

At Critical Point, phase boundaries vanish as it is defined by Critical Temperature & Critical Pressure.

Triple Point

The temperature & Pressure at which three phases (gas, liquid & solid) of substance coexist in thermodynamics equilibrium.

Clausius-Clapeyron Equation

Express relationship between vapour pressure & absolute temperature of liquid to calculate mean heat of vapourisation of liquid

Define mean heat of vapourisation.

Heat absorbed by 1 mole of liquid when it passes into vapour phase.

Phase Rule

F = C - P + 2, where F is degrees of freedom.

Define no. of degree of freedom.

Least number of intensive variables (Temperature, pressure, concentration & etc.), which must be fixed to describe system completely.

Eutectic Point

The lowest temperature at which a mixture of components will melt.

Applications of Phase Equilibrium

Lyophilization (freeze-drying) for preserving drugs sensitive to heat/moisture.