Physical Chemistry

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Phase rule

One component system

2] Sulphur System

Sulphur exists in four phases ie rhombic sulphur, monoclinic sulphur, liquid sulphur and vapour sulphur.

Sulphur rhombic and sulphur monoclinic are allotropes of sulphur.

Sr - Rhombic sulphur

Sl - Liquid sulphur

Sm - Monoclinic sulphur

Sv - sulphur vapours

In phase diagram of sulphur system we have

Six Stable curves (OB,OA,AE,OC,AC,CF)

Four areas (BOCF,OAC,FCAE,BOAE)

Four metastable curve (GO,OD,DA,DC)

Three triple point (O,A,C)

Point O ( T=95.6°C and P=0.006mmHg)

On point 'O' Three phases are in equilibrium ie

Sr ⇌ Sm ⇌ Sv

Point A (T=120°C and P=0.04mmHg)

On point A Three phases are in equilibrium ie

Sm ⇌ Sl ⇌ Sv

Point C (T=151°C and 1288 atm)

On point C Three phases are in equilibrium ie

Sr ⇌ Sm ⇌ Sl

Metastable triple point (D)

(T=115°C and P=0.03mmHg)

On the point D three phases are in equilibrium ie

Sr ⇌ Sl ⇌ Sv

By applying phase rule for triple point and metastable triple point we get

F=C-P+2       (C=1 and P=3)

F=1-3+2

F=0 

Hense the system on triple points and metastable triple point is inonvariant or invariant or zerovariant.




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