基础化学_09 iquids

1 Chemistry for engineering liquids Silvia Bodoardo 1 2 Chemistry for engineering liquids Silvia Bodoardo 2 • definition • intermolecular bonding • surface tension e vapour tension • different matter state CONTENTSCONTENTS 3 Chemistry for engineering liquids Silvia Bodoardo 3 Low distance between particles Bonds stronger than those between gas particles. Kinetic energy lower than gas but hugher than crystals 4 Chemistry for engineering liquids Silvia Bodoardo 4 INTERMOLECULAR BONDINGINTERMOLECULAR BONDING Interactions between molecules Dispersion (London) N2----- N2 Induced dipole N2----- HBr dipole-dipole HBr---- HBr Hydrogen bond H2O ---H2O HF NH3 H H H HO O In creasin g b o n d stren g h t Van der Waals 5 Chemistry for engineering liquids Silvia Bodoardo 5 IntermolecularIntermolecular bondingbonding dipole - dipole + - + - + - + - + -+ - + - + - + - + - + - + - + - + - 6 Chemistry for engineering liquids Silvia Bodoardo 6 dipole – induced dipole - + - + Es: HBr-N2 Dispersion London Es: N2-N2 - ++ -- ++ -- ++ -- ++ -- + - + 7 Chemistry for engineering liquids Silvia Bodoardo 7 HydrogenHydrogen bondingbonding PM SnH4 0 -100 -200 GeH4SiH4 CH4 SbH3 AsH3PH3 NH3 HI HBr HCl HF H2TeH2SeH2S H2O B o i l i n g p o i n t ° C 100 8 Chemistry for engineering liquids Silvia Bodoardo 8 When H-bond? The electronegativity difference has to be high (F-H ~ 2; C-H ~ 0.5) H is bonded to a small atom H H H Hδ+ δ+ δ+ δ+δ-δ- δ - δ- H-bond is an intermolecular bond whose strenght is intermediate between covalent bond and Van der Waals bonds H-bond in water 9 Chemistry for engineering liquids Silvia Bodoardo 9 10 Chemistry for engineering liquids Silvia Bodoardo 10 11 Chemistry for engineering liquids Silvia Bodoardo 11 12 Chemistry for engineering liquids Silvia Bodoardo 12 Some Some examplesexamples 13 Chemistry for engineering liquids Silvia Bodoardo 13 14 Chemistry for engineering liquids Silvia Bodoardo 14 SUPERFICE TENSIONSUPERFICE TENSION A liquid drop presents a spheric shape when it is in vacuum a) If it lies on a solid it becomes a spherical cap b). a) b) The liquid surface tends to have the smallest possible surface area The surface tension is the energy required to increase the surface area by a unit amount. The stronger are the forces between the particles in the liquid, the greater the surface tension. 15 Chemistry for engineering liquids Silvia Bodoardo 15 VapourVapour pressurepressure Evaporation (physical process): ¾ reversible phase change between liquid and gas phase ¾ heat adsorption T cost.; initial vacuum 16 Chemistry for engineering liquids Silvia Bodoardo 16 Gas-liquid equilibrium 17 Chemistry for engineering liquids Silvia Bodoardo 17 � it depends on temperature 760 Vapour pressure Vapour pressure at different temperatures: Clausius- Clapeyron equation lnp2-lnp1= Qevap /R (1/T1 –1/T2) The pressure exerted by the vapour in equilibrium with the liquid is the vapour pressure. 18 Chemistry for engineering liquids Silvia Bodoardo 18 Ô boiling point Ô critical temperature for H2O: Tc 374 °C a 218 atm Teb dipends on vapour pressure At boiling point the vapour pressure P1 is equal to the external pressure P2 19 Chemistry for engineering liquids Silvia Bodoardo 19 PHASE CHANGESPHASE CHANGES temperature time solid liquid gas Tm Tb melting boiling 20 Chemistry for engineering liquids Silvia Bodoardo 20 21 Chemistry for engineering liquids Silvia Bodoardo 21 PhasePhase ChangesChanges solid liquid gas freezing Vapori- zation melting conden- sation Sublima- tion Deposi- tion 22 Chemistry for engineering liquids Silvia Bodoardo 22 ONE COMPONENT PHASE DIAGRAMSONE COMPONENT PHASE DIAGRAMS The phase diagram is divided in three zones corresponding to the field of stability fo the solid, of the liquid and of the vapour. These fields are delimited by curves which permit to determine the temperatures and the pressures of cohesistance of two phases in equilibrium. C critical point Triple point T 23 Chemistry for engineering liquids Silvia Bodoardo 23 Some substances can be present in different crystalline forms depending on temperature and pressure: allotropism Fe α ccc ferrite α Fe γ cfc austenite Fe δ ccc 24 Chemistry for engineering liquids Silvia Bodoardo 24 Fe pure p= 1 atm