H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 1 Chapter 21 Phase Equilibrium I: One-Component Systems 21.1Definition of a Phase 21.2Phase Equilibrium 21.3Phase Diagram for One- Component System

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 2 Definition of a phase Phase Any part of a system which is physically separated from other parts of the system by a distinct boundary. A phase can be a solid, liquid, vapour (gas) or aqueous solution which is uniform in both chemical constitution and physical state Definition of a Phase (SB p.248)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 3 Heterogeneous system ---- system with more than one phase Homogeneous system ---- system consists of one phase only 21.1 Definition of a Phase (SB p.248)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Definition of a Phase (SB p.249) Type of systemSystemExampleNumber of phases HomogeneousMixture of gasesAir (mixture of N 2, O 2, CO 2 …) 1 gaseous phase HomogeneousMixture of two miscible liquids Ethanol and water 1 liquid phase HomogeneousMixture of two immiscible liquids Salt and sand2 solid phases HomogeneousMixture of two solids Ice and water1 solid phase and 1 liquid phase The phases of various systems

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Definition of a Phase (SB p.249) The phases of various systems HeterogeneousMixture of a solid and a liquid Ice, water and vapour 1 solid phase, 1 liquid phase and 1 gaseous phase HeterogeneousMixture of a solid, a liquid and a gas Ice, water and vapour 1 solid phase, 1 liquid phase and 1 gaseous phase HeterogeneousMixture of two solids and a gas CaCO 3, CaO and CO 2 2 solid phases and 1 gaseous phase

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 6 Phase Equilibrium A phase equilibrium is a balance between phases, that is the coexistence of two or more phases in a state of dynamic equilibrium Phase Equilibrium (SB p.249)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 7 We will discuss phase equilibrium for: Two component systems (Chapter 22) Two component systems (Chapter 22) Three component systems (Chapter 23) Three component systems (Chapter 23) One component systems (Chapter 21) A component is a chemical species which may be used to specify the composition of a system Phase Equilibrium (SB p.249)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Phase Equilibrium (SB p.250) SystemPhaseComponent Number of components An ice block1 solid phaseWaterOne A bottle of perfume 1 liquid phase and 1 gaseous phase PerfumeOne A small amount of sodium chloride added to a saturated sodium chloride solution 1 solid phase and 1 liquid phase Sodium chloride and water Two Iodine in a separating funnel containing water and 1,1,1- trichloroethane 2 liquid phasesIodine, water and 1,1,1- trichloroethane Three The phases and components of various systems

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 9 At a fixed temperature (a dynamic equilibrium) A phase equilibrium 21.2 Phase Equilibrium (SB p.250) Evaporation and Condensation Saturated vapour pressure

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 10 From expt: s.v.p.  with temperature. A phase diagram 21.2 Phase Equilibrium (SB p.250) Conditions at which phase equilibria occur between liquid & vapour. Only liquid can be found Only vapour can be found

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Phase Diagram for One-Component System (SB p.251) One Component System - General

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Phase Diagram for One-Component System (SB p.252) The general features of a phase diagram Region/Line/ Point NameDynamic equilibrium RegionSolidOnly solid phase exists. LiquidOnly liquid phase exists. VapourOnly vapour phase exists LineS-L (fusion curve)Solid and liquid phases are in equilibrium. L-V (vaporization curve)Liquid and vapour phases are in equilibrium. S-V (sublimation curve)Solid, liquid and vapour phases are in equilibrium. PointT (triplet point)Solid, liquid and vapour phases in equilibrium. C (critical point)Beyond this point, the vapour cannot be changed into liquid by altering the pressure alone.

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Phase Diagram for One-Component System (SB p.252) Phase Diagram of Water TA= sublimation curve TC= vaporization curve TB= fusion curve (-ve slope for water) - unusual

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 14 T B pressure temperature An increase in pressure lowers the m.p. of water. ice Ice contracts when melted. Increase in pressure enhances melting Phase Diagram for One-Component System (SB p.252)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 15 Contraction in volume By Le Chatelier’s principle, the effect of increasing the pressure will favour a reduction in volume, causing the equilibrium to be shifted to the right. (open structure) 21.3 Phase Diagram for One-Component System (SB p.253) H 2 O(s) H 2 O(l)

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 16 TA= sublimation curve TC= vaporization curve TB= fusion curve (+ve slope for CO 2 ) - usual CO 2 Solid CO 2 expands when melted. Increase in pressure inhibits melting Phase Diagram for One-Component System (SB p.254) Phase Diagram of Carbon Dioxide

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book Phase Diagram for One-Component System (SB p.254) T above 1 atm  solid CO 2 sublimes when left in a warm atmosphere

H+H+ H+H+ H+H+ OH - New Way Chemistry for Hong Kong A-Level Book 2 18 The END