Wednesday Jan. 15• Roll sheet, please sign• Reading Quiz on 11.5-11.6• Chapter 11

– 11.1 Gases, Liquids, and Solids– 11.2 Intermolecular Forces– 11.3 Select Properties of Liquids– 11.4 Phase Changes– 11.5 Vapor Pressure– 11.6 Phase Diagrams

Reading for next Wednesday January 22

Sections 13.1-13.3

There will be a Reading Quiz at the beginning of class.

Pre-Class Reading Assignment

Chapter 11 Homework

• Problems, 9, 15, 17, 19, 21, 23, 25, 27

• 33, 35, 39, 45, • Do these problems for Friday but

don’t turn them in• 7, 49, 51, 53, 55, 57, 59, 61, 73

Quiz on 9 – 45 Friday Jan 17 in class.

1) Add up the total number of electrons: 2) Draw the skeleton structure: 3) Distribute the valence electrons around the atoms until each atom has a complete valence shell (eight valence electrons): 4) Add the remaining electrons to the central atom (S): 5) Check to make sure that the central atom has a complete octet.  In this case, the S atom has only 6 of the 8 required electrons.  Therefore, we must remove one of the nonbonding electrons around one of the O atoms and create a double bond between that O atom and the S atom:

This, however, raises one question.  From which O atom do we remove the nonbonding electrons to form the double bond.  The two structures below are basically the same except for the choice of the oxygen atom with which the S atom forms the double bond.

Actually, both of these structures are incorrect.  They both suggest that one bond (the double bond) in the molecule is stronger than another (the single bond) which is untrue.  The two S-O bonds are equally strong.  This introduces the concept of resonance hybrids.

Phase Changes

DH fus

DH fus

DH vapDH vapDH sub

DH sub

Endothermic – takesEnergy to push molecules farther apart (arrow up red)

Exothermic – energy is released (arrow down blue)

DH freezingDH condensationDH deposition

DH = H final - H initial

DH is positive

DH is negative

Energy Changes Associated with Changes of State

It takes more heat to vaporize substances than to melt them.

DH sub = DH fus + DH vap

Specific heat is the amount of heat energy necessary to increase the temperature of a given mass of a particular substance by some amount

Specific heat =heat transferred

mass temperature change

Cs =q

m T

For liquid water 4.184 J/g-K

Heating Curves

• The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other.

• The temperature of the substance does not rise during a phase change.

• BC• DE

DH fus

DH vap

DH vap

DH fus

Sample Ex 11.3

Part A

1.00 mole of ice at -25C to steam at 125 constant pressure 1 atm

Part B

DH• 100g water cooled to

ice at -30.0 oC

Specific heat• H2O(s) 2.03J/gK

• H2O(l) 4.184J/gK

• H2O(g) 1.84J/gK

DH fus 6.01kJ/mol DH vap 40.67kJ/mol

Vapor Pressure – pressure exerted by a vapor in equilibrium with a solid or liquid phase at a given temp

• Closed system

Vapor Pressure is Temperature Dependent

• At any temperature some molecules in a liquid have enough energy to break free.

• As the temperature rises, the fraction of molecules that have enough energy to break free increases.

Escape into the gas phase

Vapor Pressure

• The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure.

• The normal boiling point is the temperature at which its vapor pressure is 760 torr.

Non linear relationship between V.P. and Temp

Phase DiagramsPhase diagrams display the state of a substance at various pressures and temperatures, and the places where equilibria exist between phases.

Red curve is vapor pressure curve

Green is sublimation curve

Blue is melting curve

Low pressure

Low

tem

pera

ture

Phase Diagram of Carbon Dioxide

Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; hence CO2 sublimes at normal atmospheric pressure.

Phase Diagram of Water• Note unique properties of water:

– The critical temperature and critical pressure are quite high (due to strong IM forces in water!)

– The slope of the solid–liquid line is negative (water is unique in that the solid phase is LESS dense than the liquid! Water expands upon freezing! See Figure 11.11 for the explanation why.)

Intermolecular Forces

Chapter 11 Homework

• Problems, 9, 15, 17, 19, 21, 23, 25, 27

• 33, 35, 39, 45, • Do these problems for Friday but don’t

turn them in• 7, 49, 51, 53, 55, 57, 59, 61, 73

Quiz on questions 9 – 45 Friday Jan 17 in class.