SISTEM EUTEKTIK
(Kesetimbangan Padat – Cair)
Dr. Mohammad Masykuri, M.Si.
Chemistry Education Study Program Teacher Training and Education Faculty Sebelas Maret University (UNS)
Website: http://masykuri.staff.fkip.uns.ac.id, email: [email protected]
Kimia Fisika 2
Modul 10
Modul 10
Syarat Sistem Eutektik
Kesetimbangan Padat – Cair dimana:
• Cairannya (A dan B): saling larut dalam semua komposisi
• Padatannya (A dan B): tidak saling larut
Diagram Sistem Eutektik
T(°C)
Mole Fraction B
0 1
Solid A + Solid B (p=2)
e (Eutectic) Liquid + A
(P=2)
Liquid + B (P=2)
Liquid (P=1)
a1 a2
a3
a4
a5 b3
a5' a5"
Liquid-Solid Phase Diagrams
• Liquids miscible & solids immiscible
• Consider Cooling along isopleth from a1
– At a2 pure B starts to come out of solution – At a3 solution is mixture of B + Liquid with
composition b3 (ratio by lever rule) – At a4 liquid has composition “e” and
freezes
• In solid region there are two phases pure A and pure B
– Composition given by tie line, ratio by lever rule
• “e” is called a eutectic
T(°C)
Mole Fraction B
0 1
Solid A + Solid B (p=2)
e (Eutectic) Liquid + A
(P=2)
Liquid + B (P=2) Liquid
(P=1)
a1
a2
a3
a4
a5 b3
a5' a5"
Examples of Simple Eutectic Systems
Component
A T m of A
(K) Component
B T m of (K) B
Eutectic
Mol %B Eutectic T m B (K)
Picric Acid 395 TNT 353 64 333
Sb 903 Pb 599 81 519
Cd 594 Bi 444 55 417
KCl 1063 AgCl 724 69 579
Si 1685 Al 930 89 851
Eutectics
• In previous diagram, the eutectic (easily melted, Gr.) point is a temperature at which a mixture freezes without first
depositing pure A or B
– Like a melting point in that it it is a definite temperature
• That’s because, since C=2 and P=3, by Phase rule, F’=0
– A cooling (or heating) curve will have a halt at the eutectic temperature
• If pure A and pure B are in contact a liquid will form at the eutectic temperature
• Examples
– solder lead/tin (67/33) melting point 183°C
– NaCl and water (23/77) melting point -21.1°C
Liquid-Solid Phase Diagrams - Reacting Systems
Solid
Compound +
Liquid
T(°C)
Mole Fraction B
0 1
a1 a2
a3
a4
a5 a5"
Liquid (P=1)
Solid A +
Liquid
Solid
Compound +
Liquid
Solid A +
Solid Compound
Solid B +
Solid Compound Solid B +
Liquid e1
e2
Liquid-Solid Phase Diagrams - Reacting Systems
• Some Binary systems react to produce one (or more) compounds
– Definite composition – Unique melting point
• Congruent melting point, I.e.
melts to a liquid of identical composition
– Maximum in phase diagram – Phase diagram interpreted as
before except now there are additional regions
Solid Compound + Liquid T(°C)
Mole Fraction B
0 1
a1 a2
a3
a4
a5 a5"
Liquid (P=1)
Solid A + Liquid
Solid Compound + Liquid
Solid A +
Solid Compound
Solid B +
Solid Compound Solid B + Liquid e1
e2
Liquid-Solid Phase Diagrams - Reacting Systems (Incongruent Melting)
T(°C)
Mole Fraction B
0 1
a1
a2
a3 a4
Liquid (P=1)
Solid A +
Liquid
Solid
Compound +
Liquid
Solid A +
Solid Compound
Solid B +
Solid Compound Solid B +
Liquid
e1
Compound Composition
b1
b2 b3 b4
p =Peritectic point
b5
Liquid-Solid Phase Diagrams - Reacting Systems (Incongruent Melting)
• If the compound is not stable as a liquid incongruent melting occurs
– Compound melts into components – Called the peritectic melting point
• One solid phase “melts around”
the other
• Isopleths – “a”
• a1-> a2 liquid phase with A + B
• a2 solid B precipitates
• a3->a4 Solid B + compound
– “b”
• b2-> b3 liquid phase with A + B
• b3 B reacts to form compound
• b3->b4 Solidcompound + liquid
• b5 solid A precipitates with
T(°C)
Mole Fraction B
0 1
a1
a2
a3 a4 Liquid (P=1)
Solid A + Liquid
Solid Compound + Liquid
Solid A +
Solid Compound
Solid B +
Solid Compound Solid B + Liquid
e1
Compound Composition b1
b2 b3 b4 p =Peritectic point
b5
