One component system

One component system

1. One Component System

2. A rule relating the possible numbers of phases, constituents, and degrees of freedom in a chemical system . Equation F=C-P+ 2 Phase Rule

3. The Phase R ule Equation

4. The least number of variable factor (pressure, temperature)which must be specified so that the remaining variable fixed automatically and the system is completely defined Example A system with F= 1 is univariant having one degree of system. Degree of Freedom

5. The least number of independent chemical constituents in terms of which the component of every phase can be expressed by means of a chemical equation Example Water system has one component i.e. water component

6. Any homogenous part of system having all physical and chemical properties the same through out. Example Liquid Vapour Phase

7. Three cases may arise

8. When one phase present System is bivariant . System is completely defined by two variable ... When two phase present System is monovariant . When three phase is present. System is non variant . This condition is attained at definite temperature and pressure . Usually shown by triple point .

9. A phase diagram is a plot showing the condition of pressure and temperature under which two or more physical states can exist together in a state of dynamic equilibrium. Phase diagram

10. Salient feature of phase diagram

11. Phase diagram is divided into three areas . Solid COB Liquid AOC Vapour AOB Each single phase has two degree of freedom. Each area of phase diagram represent a bivariant system. AREAS

12. PHASE DIAGRAM

13. C urves

14. The three boundary lines enclosing the three areas on the phase diagram intersect at a common point called the triple point. At triple point all the three phases can co exist in equilibrium. Solid liquid vapour Degree of freedom is zero at triple point. Triple point

15. Metastable equilibrium The Vapour pressure curve OA terminate at O when the liquid freezes. By carful cooling of the liquid under condition under condition that crystal are not form the curve OA can be extended to A’. The liquid can be cooled far below than it’s freezing point with out separation of crystal. On slightly disturbance as introduction of a seed crystal ,the entire liquid solidifies. Dashed curve OA’ Represent metastable equilibrium.

16. Super cooled liquid Vapour Vapour This system at once reverts to true stable system Solid Vapour The vapour pressure of metastable phase is always higher than that of the stable phase at same pressure.

17. POLYMORPHISM ALLOTROPY AND ITS TYPES

18. The occurrence of the same substance in more than one crystalline form is known as polymorphism. This phenomena is shown by both element and compound. In case of elements the term allotropy is often used . They have similar chemical properties but different physical properties . Polymorphism

19. Existence of an element into more than one physical forms is known as allotropy. ALLOTROPY Example

20. Allotropy has three types which are as follows. Types of allotropy

21. When the change of one form to the other at the transition temperature is reversible the phenomenon is called enantiotropy. Example Enantiotropy α Sulphur β Sulphur (Rhombic S ulphur) (Monoclinic Sulphur) T hus alpha sulphur and beta sulphur are enantiotropy.

22. These crystal which are short and flat diamond like structure.they are formed under 96 degree centigrade. Monoclinic sulphur These crystal which are long and thin rectangular. T hey are formed a bove 96 degree centigrade. Monotropy It occurs when one form is stable and the other is metastable. Rhombic S ulphur

23. Graphite Diamond Graphite is stable and diamond is metastable. Dynamic allotropy The separate forms usually have different molecular formula but the same empirical formula. This form of allotropy known as dynamic allotropy. Example

24. EXPERIMENTAL DETERMINATION OF TRANSITION POINT

25. Definition The temperature at which a polymorphic substance changes from one form to another is known as transition temperature or transition point. EXAMPLE Rhombic sulphur is converted to monoclinic sulphur at 95.6 ºC. Experimental determination of transition point

26. Determine by measuring change in physical properties.

27. If a little mercury(II) iodide is placed in a melting point attached to thermometer and heat in some form of apparatus. Red mercury(II) iodide changes to yellow form. Colour Change

28. When rhombic sulphur changes to monoclinic sulphur there is decrease in density and increase of volume. The increase in volume is employed to measure transition temperature by using apparatus Dilatometer. Density Change

29. Some powered sulphur is introduced in glass bulb and liquid paraffin a bove the sulphur. The apparatus is placed in water bath and temperature is raised. The scale reading and temperature is recorded every minute. A plot of liquid level in capillary against temperature gives a curve. On cooling of the dilatometer reverse changes take place. The transition temperature is taken as the mean of respective temperature. Method

30. Two forms of same substance have different solubilities but at the transition point they have identical solubility. If solubility temperature graph plotted it consist of two parts with a sharp break. At the meeting point of two curves the solubility of two form is same and it indicates the transition temperature. Example Na2SO4 and Na2SO4.10H20 Solubility change

31. When one form passes to another there is evolution or adsorption of heat. Let A converted to B on heating. Let B to cooled and a curve obtained by plotting temperature against time. Steady curve has a distinct break at a temperature corresponding to the transition point. Cooling curve method

32. Suitable for determining the transition temperature. Between different hydrates of salt or between a hydrate and anhydrous salt or for different forms of metal. Importance

33. WATER SYSTEM

34. Water is the three phase one component system the three phase involved are

35. The number of phases which can exist in equilibrium any time depends on condition of temperature and pressure SALIENT FEATURE OF PHASE DIAGRAM The curves 0A,OB,OC. The triple point O. The areas AOC,AOB,BOC.

36. It represent the vapour pressure of liquid water at different temperature. Water and vapour co-exist in equilibrium along this curve. The curve OA terminates at A the critical point(218atm,374 ºC). CURVE OA , the V apour P ressure C urve of Water

37. It shows the vapour presssue of solid ice at different temperature. The two phase solid ice and vapour co-exist in equilibrium along this curve. At the lower limit the curve 0B terminate at obsolute zero(-273 ºC)where no vapour exist. Curve OB The S ublimation C urve of Ice

38. The Phase D iagram of the System W ater

39. It depicts the effect of pressure on the melting point of ice.Here ice and water co exist in equilibrium. The fact O C slopes to the left indicates that the melting point of ice decreases with increase of pressure. Curve OA,OB,OC there are two phase in equilibrium and one component. F =C-P+2 1-2+2=1 Curve OC, The F usion C urve of Ice

40. Water/water vapour represented by OA . Ice/water vapour represented by OB . Ice/water represented by OC . It is mono variant. The triple point “O” The curves OA OB and OC meet at triple point O where all three phases are in equilibrium. Here are three phases and one component system. F =C-P+2 1-3+2=0

41. Area AOC, AOB, BOC The system is bivariant i.e has 2 degree of freedom . The system at “ O “ is non variant thus if pressure or temperature is changed the three phases would not exist and one of the phase disappear.

42. Water can be super cooled by carefully eliminating solid particle. The super cooled water/ vapour system is metastable. It once reverts to the stable system ice/ vapour on the slightest disturbance or introducing a crystal of ice . Metastable system

43. Sulphur System

44. Four Phases are as follows

45. The two crystalline form of sulphur rhombic sulphur and monoclinic sulphur exhibit enantiotropy with a transition point 95.6 degree centigrade. Rhombic sulphur monoclinic sulphur liquid sulphur (95.6) (120)

46. Salient feature of phase diagram

47. Sulphur system phase diagram has four areas. Rhombic sulphur. ABG Monoclinic sulphur. BEC Liquid sulphur. GECD Sulphur Vapour. ABCD Each represent single phase. Degree of freedom is two i.e bivariant Area

48. SULPHUR SYSTEM PHASE DIAGRAM

49. Six curves AB,BC,CD,BE,CE,EG Curve AB Vapour pressure curve of Rhombic sulphur Curve BC Vapour pressure curve of monoclinic sulphur Curve CD vapour pressure curve of liquid sulphur Curve BE transition curve Curve CE fusion curve of monoclinic sulphur Curve EG fusion curve for Rhombic sulphur C urves

50. Along this curve two phase rhombic sulphur and sulphur Vapour co exist and are in equilibrium. Have one degree of freedom Along this curve monoclinic sulphur and vapour sulphur co –exist. Shows variation of vapour pressure of monoclinic sulphur with temperature. Curve AB Curve BC

51. Shows of variation of Vapour pressure of liquid sulphur with temperature. Along CD liquid sulphur and sulphur Vapour are in equilibrium. It has degree of freedom one. 1 atm line meet at temperature 444.6 which is boiling point of sulphur Curve CD

52. Increase in pressure will shift the equilibrium to the left (Le chatelier’s principle) and the transition temperature will raised. BE slopes away from pressure axis. Along curve Monoclinic and liquid sulphur co exist Shows increase of pressure will increase the melting point and volume increase Slope CE away from pressure axis The curve end at E because monoclinic sulphur ceases to beyond this limit . Curve CE

53. Show effect of pressure on transition temperature for rhombic and monoclinic sulphur. Along this curve rhombic and monoclinic sulphur are in equilibrium The system is monovariant The transformation of rhombic sulphur and monoclinic sulphur is due to increase of volume and absorption of heat . Curve BE transition curve

54. Rhombic and liquid sulphur co exist in equilibrium Degree of freedom is two Curve EG Fusion Curve For Rhombic Sulphur

55. There are three triple point in sulphur system which are as follows. Triple point at B. Triple point at C. Triple point at E . Triple point

56. A phase that can be produced by a very rapid change in system conditions( temperature, pressure)or in some case The metastable state may persist indefinitely as the movement towards equilibrium is virtually imperceptible over long period of time. Meta stable equilibrium

57. If enough time for the change is not allowed and rhombic sulphur is heated rapidly It is possible to pass well above the transition point with out getting monoclinic sulphur. In that case phase diagram will consist of Three curves One triple curve Three areas (rhombic sulphur,liquid sulphur,sulphur Vapour )

58. Continuation of vapour pressure curve AB of stable rhombic sulphur. The metastable phase rhombic sulphur and sulphur vapour are in equilibrium. It has one degree of freedom. The Vapour pressure curve of supercooled liquid sulphur Dashed curve BF,Vapour pressure curve of metastable rhombic sulphur

59. Curve CF, Vapour pressure curve of super cooled liquid sulphur On super cooling liquid sulphur, dash curve CF is obtained Metastable equilibrium between liquid sulphur and sulphur Vapour Dashed curve FE, the melting curve of metastable of Rhombic sulphur The two metastable phase rhombic sulphur and liquid sulphur are in equilibrium. Melting point of rhombic sulphur increase with pressure.

60. At this point, three metastable phases rhombic sulphur,liquid sulphur and Vapour sulphur are in equilibrium. The system is a metastable triple. With no triple point. Metastable triple point O