Previously in Chem 104: unit cell, Z, at.wt related to density Ionic Unit Cell types of closest packing, ccp= fcc, hcp Al not so stable! TODAY QUIZ anwer key out - send self-check by Tuesday 5PM examples of molecular solids Born Haber Cycles “why doesn’t that solid exist” phase diagrams

Born Haber Cycles Relate Lattice Enthalpy and Heat of Formation  H f Must be (-) for a stable solid ionic solid Elements in Standard States: M(s), X 2 (g) Energy

Born Haber Cycles  H f must be (-) for a stable solid ionic solid, MX M(s), X 2 (g) Energy M + (g), X - (g) M + (g) M(g) X - (g) X (g)  H sub  H I.E.  H BD  H lattice  H EA

Born Haber Cycles ionic solid, MX M(s), X 2 (g) Energy M + (g), X - (g) M + (g) M(g) X - (g) X (g)  H sub  H I.E.  H BD  H lattice  H EA  H f =  H sub +  H I.E +  H BD +  H EA +  H lattice HfHf

Born Haber Cycles ionic solid, MX M(s), X 2 (g) Energy M + (g), X - (g) M + (g) M(g) X - (g) X (g)  H sub  H I.E.  H BD  H lattice  H EA  H f =  H sub +  H I.E +  H BD +  H EA +  H lattice HfHf For NaCl: -381 = –

 H f =  H sub + DH I.E +  H BD +  H EA +  H lattice For NaCl: -381 = – For NaO: +600 = ½ (493) Positive  Hf: NaO does not (can not) exist! For Al 2 O 3 : = 2( ) + 3/2 (493) + 3 (639) - 15,600

Solids and Phase Diagrams. Temperature, T Pressure, P Energy

The Basics of a Phase Diagram Temperature, T Pressure, P solid liquid gas What does the slope of this line tell us? Triple point:

H 2 O Phase Diagram Temperature, T Pressure, P solid liquid gas

CO 2 Phase Diagram Temperature, T Pressure, P solid liquid gas

Fe-C (steel) Phase Diagram (Fe 3 C) Steel (BCC) FCC Cast Iron