chapter 10: liquids solids intermolecular...

CHAPTER 10: LIQUIDS + SOLIDS

INTERMOLECULAR FORCES

GENERALITIES

DIPOLE-DIPOLE FORCES

HYDROGEN BONDS

H Cl H Cl HC

H

O HC

H

O

HO

H

HO

H HN

H

H

HN

H

H

H F H F

HO

H

HO

HH

OH

LONDON DISPERSION FORCES (LDF)

Electronic orientations at different times Temporarily induced dipoles

Helium is a liquid at 4 Kelvin Methane (CH4) is a liquid at –160 ˚C

Titan (Saturn’s largest moon) has liquid CH4 rivers, oceans, and rain.

Sample Problems:

Identify the IMF pointed to by an arrow. Use a dashed line to show the strongest IMF possible between these two molecules. Also identify the IMF.

IMF: IMF:

He HeHe

HC

H

H H

HC

H

H H

I Cl I ClC

NH

H

H

HH

OH

H

BOILING POINT

BOILING PROCESS + DHvap

Liquid H2O (water) Which of these represents gaseous H2O (steam)?

→

Boiling (liquid to gas) involves…

Heat of Vaporization (DH˚vap):

Water DHvap = +40.7 kJ/mol

BOILING POINT TRENDS

Molar Mass (g/mol)

DH˚vap (kJ/mol)

Boiling Point (˚C)

O2 32.00 6.8 –183.0

F2 38.00 6.6 –188.1

Cl2 70.90 20.4 –34.0

Br2 159.80 30.0 58.8

Bromine (liquid/gas); Chlorine (gas only)

liquid

Molar Mass (g/mol)

DH˚vap (kJ/mol)

Boiling Point (˚C)

Methanol

(CH3OH)

IMF:

32.05 38.3 64.7

Formaldehyde

(CH2O) IMF:

30.03 23.3 –19.2

Ethane

(CH3CH3) IMF:

30.08 14.7 –88.6

Sample Problems:

In each pair, determine which should have the higher boiling point, and explain the trend using intermolecular forces.

HCl vs. HF Propane (C3H8) vs. Pentane (C5H12)

HC

O

H H

H

HO

CH

H H

HC

H

O HC

H

O

HC

C

H H

H

H H

HC

C

H H

H

H H

LIQUID PROPERTIES

SURFACE TENSION

Water beading on waxy surface Scott Kelly with water droplet in space Water skipper

CAPILLARY ACTION

Concave meniscus with water Convex meniscus with mercury

GlassO

Si

OH

H

H

O HHO

HSurface

VISCOSITY

Honey is viscous Structure of sugar (sucrose, C12H22O11)

“Pitch drop experiment” with asphalt / tar General structure of tar / crude oil

Sample Problems:

Which liquid is the most viscous?

Glycerin (glycerol) 1-propanol 2,4-pentanedione

O

CC

C

CC

C

CC

C

O

O

C HO

H HH

HO

H

OH O

H

H

H

HC

H

OH H

H

OH

O

H

H

C

OH

HH

H

OC

CC

O

O

H

H

H

H H H H

HH

CC

CO

H

H H H H

H HC

CC

CC

H

O O

H H

H

HH

HH

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

60-70 of these!

EVAPORATION

EVAPORATION

VAPOR PRESSURE

Sample Problem:

Equal volumes of liquids A and B are placed in separate beakers on the countertop.

a. After some time, half of “A” has evaporated. After the same amount of time, should there be more or less of “B” remaining?

b. Which has a higher vapor pressure, A or B?

CC

C

O

H

HH

H

HH C

CC

C

H

HH

H

HH

H H

A B

TEMPERATURE + VAPOR PRESSURE

Temp H2O (˚C)

Vapor Pressure H2O (torr)

0 4.6 20 17.5 40 55.3 60 149.4 90 525.8 100 760.0

LINEAR RELATIONSHIP

Inverse Temp (K–1)

Natural log (ln) of Vapor Pressure

H2O 0.00366 1.52 0.00341 2.864 0.00319 4.013 0.00300 5.0066 0.00275 6.2649 0.00268 6.6333

Logarithm Review:

log (100) means 10? = 100 log (100) = 2 because 102 = 100

ln (7.39) means e? = 7.39 ln (7.39) = 2 because e2 = 7.39

m = –5204 b = 20.6

Water, bp = 100 ˚C

Clausius-Claperyon Equation

ln$𝑃&'() = −∆𝐻&'(𝑅 /

1𝑇2 + 𝑐

ln 567689 =

∆:;<=>

5 ?@8− ?

@79

ln = natural log (base “e”, not base 10) Pvap = vapor pressure DHvap = heat of vaporization (J/mol) R = gas constant, 8.3145 J/mol·K T = temperature in Kelvin

P1 = vapor pressure at temperature 1 P2 = vapor pressure at temperature 2 T1 = Kelvin temperature 1 T2 = Kelvin temperature 2

Sample Problems:

Give the graphical data for water, calculate water’s heat of vaporization in kJ/mol. (Note: actual DHvap water = +40.7 kJ/mol.)

The vapor pressure of alcohol (ethanol) at 34.7 ˚C is 100.0 mmHg, and the heat of vaporization of alcohol is 38.6 kJ/mol. Calculate the vapor pressure of alcohol at 65.0 ˚C.

m = –5204 b = 20.6

The normal boiling point of acetone is 56.5 ˚C. At the Donner Summit (~7200 ft) on Highway 80 on the road to Reno and South Lake Tahoe, the atmospheric pressure is 585 mmHg.

a. At the normal boiling point, what is the vapor pressure of acetone?

b. When acetone is boiling at Donner Summit, what is its vapor pressure?

c. What is the boiling point (in K and ̊ C) of acetone (DHvap = 32.0 kJ/mol) at Donner Summit?

MULTIPLE PHASE TRANSITIONS

HEATING CURVE

Phases Water Water / steam Water / steam Steam Steam

Temp (˚C)

Sample Problem:

Calculate the amount of energy (as heat) needed to boil 50.0 g of water at 100.0 ˚C.

What is the q of the opposite process (100.0˚C steam to 100.0 ˚C water)?

For H2O: sice = 2.03 J/g˚C swater = 4.184 J/g˚C ssteam = 2.06 J/g˚C DHvap = 40.7 kJ/mol DHfus = 6.02 kJ/mol

q = swater·m·DT

q = sice·m·DT

q = ssteam·m·DT

solid

liquid

gas q =

q =

Sample Problem:

Calculate the heat energy (q) associated with bringing 50.0 g of ice at –10.0 ˚C to its boiling point.

PHASE DIAGRAMS

Melting: Boiling: Sublimation:

Freezing: Condensing: Deposition:

Triple Point:

Critical Point:

Supercritical Fluid:

Phase Diagram for Propane (C3H8) Phase Diagram for Carbon

gas

100500–50–100–150–2000

10

20

30

50

40

liquid

solid

Pres

sure

(bar

)

Temperature (˚C)

supercritical fluid

Piece of “dry ice” (solid CO2)

Sample Problems:

1. At which point(s) on the phase diagram do the following exist? Liquid only __________

Both solid and liquid __________

A supercritical fluid __________

2. If the substance is at point “b” and the

pressure is lowered without changing the temperature, what will eventually happen? a. It will melt b. It will freeze c. It will boil d. It will condense

SOLIDS

BROAD CATEGORIZATION

Obsidian (glassy SiO2) Quartz (crystalline SiO2)

Amorphous solid:

Crystalline solid:

Crystalline “lattice”

2-D PACKING IN CRYSTALLINE SOLIDS

Packing Efficiency = A('BCD'ECFGH('IDJBKCAA('BC'&'JK'GKCJFLFJDBCKK

× 100

Coordination Number =

3-D PACKING IN CRYSTALLINE SOLIDS

Simple Cubic Body-Centered Cubic Face-Centered Cubic

Unit Cell

Examples Polonium (very few examples)

Iron, Chromium, Tungsten, Niobium, Uranium

(very common)

Lead, Aluminum, Copper, Gold, Silver

(very common)

Sample Problems:

Calculate the packing efficiency for crystalline lead, which adopts a face-centered cubic (fcc) unit cell.

Packing Efficiency = ('IDJBKC&MKLNCLFJDBCKK&MKLNC

× 100

Calculate the length of one side of the unit cell of crystalline gold, which adopts a face-centered cubic (fcc) arrangement. The radius of a gold atom is 135 pm, where 1 × 1012 pm = 1 m.

Pythagorean theorem

a2 + b2 = c2

c

b

a

UNIT CELL SUMMARY – AFTER ACTIVITY

Simple Cubic (sc)

Body-Centered Cubic (bcc)

Face-Centered Cubic (fcc)

Coordination Number

Packing Efficiency

Length of unit cell

METAL ALLOYS

Substitutional alloy: different elements replace (substitute) each other in the crystal lattice.

Brass: alloy of copper and zinc (often 2:1); exist as mixtures of face-centered / body-centered cubic.

Bronze: alloy of copper and tin (often 88% Cu, 12% Sn).

Interstitial alloy: other elements fit in the cracks (“interstices”) of the crystal lattice.

Steel: Iron in a face-centered cubic lattice, with carbon (up to 2%) in the cracks.

IONIC SOLIDS

Sodium chloride (NaCl) Ammonium chloride

METALLIC BONDING

Metal Properties:

• Conductors of electricity:

• Conductors of heat:

• Malleable:

Electron “Sea” Model:

OTHER SOLIDS

Ionic Solids Molecular Solids Network Solids Metallic Solids

NaCl

I2

diamond

Zn

NaCl, MgO, CaCl2 etc.

Ice (H2O), Dry Ice (CO2), Sugar

(C12H22O11), S8, P4

Glass, rock (SiO2), Diamond (C) Fe, Mg, Zn, etc.

m.p. NaCl: 801 ˚C

m.p. Al2O3: 2072 ˚C

m.p. sugar: ~140 ˚C m.p. sand: 1600 ˚C

m.p. diamond: 3800 ˚C

m.p. Cu: 1085 ˚C

m.p. W: 3422 ˚C

Sample Problem:

Which should have the lowest melting point?

a. Aspirin (C9H8O4) b. Sodium acetate (NaC2H3O2) c. Titanium (Ti) d. Quartz (SiO2)

chapter 10: liquids solids intermolecular...

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