EQUILIBRIUM & STABILITY, LIQUID-LIQUID EQUILIBRIUM, Chemical Engineering Department Government Engineering College Bhuj-370001 Prepared By: 140153105007-Meet Somani 140153105008-Nidhi Suvagiya 140153105009-Hardik Vaghela 140153105010-Kamlesh Vankar Guided By: Prof. : S.R.Banker EQUILIBRIUM & STABILITY, LIQUID-LIQUID EQUILIBRIUM, SOLID- LIQUID EQUILIBRIUM, OSMOTIC EQUILIBRIUM AND OSMOTIC PRESSURE B.E. (Chemical)- Sem- V Subject : CET-2 Subject Code: 2150503

Equilibrium & Stability The passage of a liquid solution from a state of a single, homogeneous phase to a biphasic LLE state occurs when a single phase is no longer thermodynamically stable. It is instructive to derive the conditions under which this may take place. Let us consider a binary liquid mixture for example for which the molar Gibbs free energy of mixing is plotted as function of mole fraction of component 1 for two temperatures At temperature the value of is always less than zero and also goes through a minimum. This signifies that the mixture forms a single liquid phase at all compositions at the given temperature. The mathematical description of this condition is given by the two following equations:

LIQUID-LIQUID EQUILIBRIA Unlike gases which are miscible in all proportions at low pressures, liquid solutions (binary or higher order) often display partial immiscibility at least over certain range of temperature, and composition. If one attempts to form a solution within that certain composition range the system splits spontaneously into two liquid phases each comprising a solution of different composition. LIQUID-LIQUID EQUILIBRIA

The straight line MYN represents a tie-line, one that connects the compositions of the two liquid phases that co-exist in equilibrium. TUCST & TLCST are called the Upper Consolute Solution Temperature (UCST) and Lower Consolute Solution Temperature (LCST) respectively.

SOLID-LIQUID EQUILIBRIA The prediction of solubility of a solid in a liquid is important for design of separation processes that utilize either preferential dissolution or crystallization as a route to purification of a species. This section is devoted to consideration of thermodynamic relations that allow computation of the solubility of solids in liquids as a function of temperature. Such relations may also be extended to estimate changes in freezing or boiling point of a liquid in presence of dissolved solids. The phase equilibria relations developed here are limited to the simplest case of systems comprising a solid (1) and a liquid (2) (solvent). As with all other phase equilibria, one starts with the basis of equality of the species fugacity in the solid (s) and liquid (l) phases respectively.

OSMOSIS Diffusion of water through the semi permeable membrane from a solution of lower concentration towards a solution of higher concentration

Osmotic Pressure and the factors on which it depends: Van‘t Hoff‘s Equation All non penetrable solutes in a solution exerts osmotic pressure According to Van’t Hoff, osmotic pressure (π) depends on the molar concentration (C) of the solution and the temperature T π = R C T where R is the gas constant

OSMOTIC PRESSURE Osmotic pressure is higher when molar concentration is higher or temperature is higher and the molecular weight is lower Osmotic pressure depends mainly on the molar concentration or molarity of a solution Osmotic pressure is a colligative property, meaning that the property depends on the concentration of the solute but not on its identity

Examples Separate pure water from a sugar solution with semi permeable membrane Both have same hydrostatic pressure Osmosis take water from side 1 to side 2 because solution on side 2 has greater pulling tendency