Chemistry 163B, Winter 2014 Lectures Introduction to Phase Diagrams

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Chemistry 63B, Winter 04 qualitative factors in phase changes Chemistry 63B One-Component hase Diagram Basics freezing/fusion vaporization condensation ENDOHERMIC EXOHERMIC sublimation

LIQUID CONSAN ALL LIQUID EVEN MORE LIQUID 3 4 vapor as heat added (vary, const ) dg for phase change at constant,, CONSAN LESS LIQUID (SOME EVAORAES) A () L A () phase phase v EQUILIB,

1 Chemistry 63B, Winter 04 qualitative factors in phase changes Chemistry 63B One-Component hase Diagram Basics freezing/fusion vaporization condensation ENDOHERMIC EXOHERMIC sublimation deposition vapor pressure over URE (notation) as pressure increases (vary, const ) * 0 NO LIQUID INCREASES CONSAN Gene E&R Raff (many others) SOME LIQUID v EQUILIB INCREASES MORE LIQUID CONSAN ALL LIQUID EVEN MORE LIQUID 3 4 vapor as heat added (vary, const ) dg for phase change at constant,, CONSAN LESS LIQUID (SOME EVAORAES) A () L A () phase phase v EQUILIB, CONSAN same, for each phase CONSAN INCREASES ALL VAOR (ALL EVAORAES) dg S Vd one component 'A' in phases and constant, dg ( ) ( ) ( ) ( ), A A A A i i i 5 dg ( ) ( ) A A ( ) ( ) ( ), A A A 6

2 Chemistry 63B, Winter 04 at () = () ; is ESCAING ENDENCY dg ( ( ( ), A A A ( ) ( ) A A, at dg = 0 dg for spontaneity dg < 0, ( ) ( ) ( ) 0, A A A 0 ( ) ( ) ( ) A A A 0 ( ) A ( ) ( ) ( ) A A A for molecules in phase molecules lost from phase molecules gained by phase is the ESCAING ENDENCY high ö low hyper ö mellow 7 Question: can my pressure cooker heat water to 00C without exploding? =98 K =0.03 bar =473 K =5.5 =???. bar 8 phase one-component systems (i.e pure substances) conditions for remaining at phase (one-component), covary and at equibrium 0 ( ) ( ) A A How can and covary to maintain? ( ) ( ),, d A() A() ( ) d ( ) ( ), d ( ) ( ),,,, ( ) ( ) ( ),, ( ) ( ), d ( ) ( ),,,, d S V d S V d d ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) with ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) d d d ( ) ( ) ( ) ( ) S V d S V d ( ) ( ) ( ) ( ) S S V V d before after 9 0 phase (one-component) I. application to V (vapor) or V V G0 S (midterm # prob 4b) ( ) ( ) ( ) ( ) S S V V d d phase S V = phase change eqn. 8.3 E&R since phase change is an (reversible) process d phase H S H V d phase H V vaporization condensation V (vapor) or sublimation deposition V V and V are small compared to Vvapor V Vvapor assume ideal V Vvapor d H H or sg dln Hvap or sub

3 Chemistry 63B, Winter 04 I. application to V (vapor) or V I. application to V (vapor) or V d or sg d ln H H H vap or sub Clausius-Clapeyron ª eqn. 8.9 E&R 3 for s or K d ln H vap or sub d ln K Hvap or sub H d ln (assume H independent of ) H E&R eqn 8.0 where is vaporization ln similar for sublimation R application to problems: normal b.p.( ), standard b.p. ( bar) to get vapor pressure given º boiling and H vap : o at = vapor = vapor H vap H vap ln R R 4 I. application to V (vapor) or V I. application to V (vapor) or V application to problems: H vap ln R to get boiling when : H vap ln R H H vap vap ln R R H R vap ln R H vap ln Hvap 5 application to problems: to get boiling when : ln Hvap Denver: elev=60m =0.8 Death Valley: elev =-8.5 m, =.00 ouch 6 II. application to V phase rule one-component system (save proof for later) d phase H V for phase at = o what is at other pressures? f f= degrees of freedom p=phases simultaneously present V V d ln H H V V ln H will increased pressure raise or lower? variables :, (same for each phase) p- restrictions: () = () = () =. f: degrees of freedom = (variables-restrictions) f = -(p-) = 3-p H > 0 (usual) V > V (when??) V < V increases decreases 7 f = 3-p phase:, vary independently phases present: 3 phases present: fixed and 8 3

4 Chemistry 63B, Winter 04 phase diagrams one component: phase vs (,) HASE BE[A]WARE: when we study multicomponent phase diagrams the axis variables may not be, 9 CO high phase, f= vary both, 0 lower phase, f= vary both, lower more CO CO high lower low raise lower more raise more 3 4 CO CO 4

Chemistry 63B, Winter 04 two-phase (p=) f= f=3-p = line (, freezing or fusion) s and s d equilib H V for phases, f=3-= d s H V fus fus 5 CO 6 phase diagrams line (vaporization, condensation) line

5 Chemistry 63B, Winter 04 two-phase (p=) f= f=3-p = line (, freezing or fusion) s and s d equilib H V for phases, f=3-= d s H V fus fus 5 CO 6 phase diagrams line (vaporization, condensation) line (sublimation, deposition) s and s for phases, f=3-= [select, then determined select, then determined] phases, f=3-= s and s for CO d H Hvap g V 7 CO d H H sub eq V 8 critical point and triple point why does ice float? riple point: for a pure substance, there is only one point (value of and ) where all three phases (,, and ) can simultaneously exist in Critical point: point (value of and ) above which and become one phase (fluid or supercritical fluid) H 0 is polar and can form hydrogen bonds (macho intermolecular forces) High surface tension and capillarity Hydrogen bonds form very open structure in H O (ice) giving ice a lower density than H O. ICE FLOAS!! movie: benzene critical point A B originally from: jchemed.chem.wisc.edu/jcesoft/cca/samples/ccabenzene.html

Chemistry 63B, Winter 04 ice bomb!!!! remember for CO : increases CO (s) CO () slope d s d s H V H 0; V Vs V 0 d 0 s ; low raise (more dense) http://www.jce.divched.

html raise more (most dense) 3 CO 3 phase diagram for water ice skater myth remember for CO : increases but for H O as increases: d slope s d WHY?

NO, not even if they are quite weighty! (not enough pressure and further details of water-ice phase diagram) V Vs ln H ) fusion V V 0 pressure ' s' ice e.g. Rosenberg, Robert (December 005).

8.7 pure H O at 98K H0= 0.036 bar Figure.

re the development of a -like surface layer at temperatures below freezing and frictional heating of the ice as skaters move around must account for ice's slipperiness at the

6 Chemistry 63B, Winter 04 ice bomb!!!! remember for CO : increases CO (s) CO () slope d s d s H V H 0; V Vs V 0 d 0 s ; low raise (more dense) raise more (most dense) 3 CO 3 phase diagram for water ice skater myth remember for CO : increases but for H O as increases: d slope s d WHY? 0 s for ice water d H s V ; H 0 Vs V V d 0 0 s H O 33 Does the weight of an ice skater create a pressure that s ice to form a groove for skate? NO, not even if they are quite weighty! (not enough pressure and further details of water-ice phase diagram) V Vs ln H ) fusion V V 0 pressure ' s' ice e.g. Rosenberg, Robert (December 005). "Why is ice slippery?". hysics oday: s E&R(3 rd ) roblem bar for -4º thin blade ; 78kgº7lb; -.5º 34 Rosenberg, Robert (December 005). "Why is ice slippery?". hysics oday: effects of inert (increased total pressure) on vapor pressure E&R sec. 8.7 pure H O at 98K H0= bar Figure. An ice skater exerts pressures on the order of a few hundred ospheres on the ice surface, enough to reduce the temperature by only a few degrees. re the development of a -like surface layer at temperatures below freezing and frictional heating of the ice as skaters move around must account for ice's slipperiness at the wide variety of subzero temperatures found in nature. (Ice Skating, by Hy Sandham, 885, courtesy of the Library of Congress he nature of the -like layer is not clear from experimental measurements, so theorists have tried to clarify the situation. 35 ( ) H O increases at total increase ( ) ( g ) HO( g) must increase to restore ( ) HO ( ) V HO ( g) total ( ) ln V d HO = bar [or+ N (g) + O (g)] normal H O in total = bar [H O (g) + N (g) + O (g)] at 98K H0 = bar 36 6

7 Chemistry 63B, Winter 04 E&R section 8.7 (effect of inert on vapor pressure ) H O at 300 K H0= 0.38 add air (inert N + O ) to raise total = End of Lecture new H0 = (/ ) H0 = triple point vary and through critical point triple point: simultaneous of, fluid 3 phases, f=3-p f=3-3=0 and fixed

Chemistry 163B. One-Component. Phase Diagram Basics

Chemistry 163B. One-Component. Phase Diagram Basics Chemistry 163B One-Component Phase Diagram Basics 1 qualitative factors in phase changes solid melting liquid freezing/fusion vaporization ENDOTHERMIC liquid gas condensation EXOTHERMIC sublimation solid