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Phase equilibrium
- Phase(P) :Matter exists in three different phases (Solid, Liquid, Gas), But, there are many solids, liquids, gases depending on their chemical nature and appearances. For example, different solids are sugar, rice, copper, etc., which are chemically different.
- Same chemical substance like water exits in different phases viz., solid (ice), liquid (water), gas (steam).
- Therefore phase is the one which is physically distinct and mechanically separable.
- Water mixed with oil will exists two phases as they are immiscible; but, water mixed with ethyl alcohol will exists in one phase as they are miscible completely.
- Component(C): It represents the minimum number of chemically independent species necessary to define the composition of all phases of the system.
- CaCO3 – CaO – CO2 system ; C= 3
- CaCO3 – CaO – CO2 system ; such that there exists an equilibrium between them as CaCO3 CaO + CO2. The number of components is then 3 – 1 = 2.
- Component (C) = Chemically independent species-No of relations between them
- Degrees freedom(F): A degree of freedom of a physical system refers to the number of parameter that is necessary to characterize the state of a physical system.
- Phase rule: F = C-P + 2
- Minimum vales for F = 0 ; C=1 & P=1
- F will be minimum when P is maximum
SOLUTION
- A Solution, has less free energy hence, is thermodynamically more stable compared to the corresponding solvent or solute.
- ∆G soln= ∆H soln -T∆S soln = -T∆S soln = -ve (decrease in free energy or less free energy)
∆H soln = 0 for an ideal solution (But, may be +ve or –ve leading to deviation from ideal behavior).
∆S soln = +ve due to mixing (for all type of solutions)- The solution, which is more stable , shows more tendencies to remain as it is. In other words, it resists evaporation (lowering of vapor pressure), resists boiling,i.e.,boils at higher temperature (elevation of boiling point) and resists freezing (depression of freezing point).
COLLIGATIVE PROPERTIES
- Colligative properties: The properties , such as lowering of vapor pressure, elevation of boiling point, depression of freezing point, osmotic pressure are called colligative properties, as they arise due to increase in entropy, collection of particles(solute) due to formation of solution.
- In fact , the colligative property: lowering of vapor pressure is the cause for other colligative properties.
- Colligative properties are properties of solvent (vapor pressure, boiling point, freezing point , osmotic pressure etc.,) modified by the number of solute molecules in the solution. Hence, they depend on the concentration of the solute (number of solute particles) and not on its nature.
- Vaporization , boiling , freezing , osmosis are phenomena related phase equilibrium.
- The solution, which is more stable , shows more tendencies to remain as it is. In other words, it resists evaporation (lowering of vapor pressure), resists boiling,i.e.,boils at higher temperature (elevation of boiling point) and resists freezing (depression of freezing point).
***The following LINK contains a file :PC-1(A): Phase Rule-Synopsis which gives a brief account of the main concepts in the subject of phase equilibrium (viz., Phase rule, Solution & Colligative properties).
Please CLICK the following LINK …↓
***The file: PC-1(B): Phase Rule ppt, in the following LINK gives an account of Phase rule as a power point presentation.
Please CLICK the following LINK …↓
***A self valuation is required by means of reflections in as many ways as possible. One such way is to know whether one has mastered the subject in terms of different terms related the subject studied . A list of terms given in the following file : PC-1(C) Phase Rule-Terms , available in the following LINK will be able to serve this purpose.
Please CLICK the following LINK …↓
***Learning, evaluation and testing are integral parts of a curriculum. They could be executed externally and practiced internally. A test paper given in the following file: PC-1(D):Phase Rule-Snap Test in the following LINK will be able to to cater this need.
Please CLICK the following LINK …↓
Please go to CONTENTS for all the Articles in PoC: Click below
https://dradchem.wordpress.com/2015/06/22/properties-of-chemistry-poc-contents-2/