Equilibrium and Stability

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Equilibrium and Stability
All irreversible processes occurring at constant
T and P proceed in a direction as to decrease in
the Gibbs energy. G is minimum at equilibrium.
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Equilibrium and Stability
For binary mixture stability requires
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Liquid-liquid Equilibrium LLE
If we mix two pure liquid species that do not
react chemically in a container, shake and bring
them to equilibrium. Observe the results. There
are 3 possibilities a) they may be totally
miscible, forming one liquid phase e.g. water and
ethanol. There is no LLE in this case b) they
may be practically immiscible, forming two liquid
phases, each of which contains only a small
amount (e.g. less than 1 mol) of the other, for
example, water and most organic compounds. c)
they are partly miscible with each other, forming
two separate liquid phases, each of which
contains substantial amount (more than 1 mol) of
the other, for example, water and some organics
like n-butanol.Which of these results occurs is
largely dependt on the molecular interactions
between the two pure species.
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Liquid-liquid Equilibrium LLE
When like (a-a and b-b) interactions are
significantly stronger than unlike (a-b)
interactions, liquid can split into two different
partially miscible phases. They form separate
phases (? and ?) to lower the total Gibbs energy
of the system.
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Liquid-liquid Equilibrium LLE
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TL lower consolute temperature lower critical
solution temperature LCST TU upper consolute
temperature upper critical solution temperature
UCST
Solubility depends on temperature
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Solid-liquid Equilibrium SLE
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High Pressure VLE