States of Matter

Phase Change DIagram

Phase Change

Water phase

changes

Temperature remains __________

during a phase change.

Phase Diagram

What is a phase diagram?

(phase diagram for water)

critical point:

beyond this point

the vapor cannot

be liquified at any

pressure

triple point: T and

P at which all

three states

coexist in

equilibrium

Normal boiling

Point: boiling

point at one

atmosphere

Normal

melting point:

melting point

at one

atmosphere

Boiling Point and Freezing Point

Review the phase diagram of

a pure substance.

How will the phase diagram

of a solution (freezing and

boiling points) differ from

those of a pure solvent?

Phase Diagram

Water Everything else

Water

Carbon dioxide Phase

Diagram for Carbon

dioxide

Carbon Phase

Diagram for Carbon

Kinetic Theory

A couple of assumptions!

Ideal Gas molecules:

Are small, hard spheres with insignificant volume

Have no attractive or repulsive forces

Move in a fast, constant, random-straight line motion

Have perfectly elastic (kinetic energy is transferred

without loss) collisions

This represents an ideal gas

Properties of Gases

Pressure (P) atm (atmospheres)

kPa (kilopascals)

Volume (V) Liters

Temperature (T) K – Kelvin

Moles (n) Number of moles

Units of Pressure, Temperature, and

Volume

Units of Pressure:

1 kilopascal (kPa) = 1000 pascals (Pa)

1 torr = 1 millimeter of mercury (mm Hg)

1 atmosphere = 760 mm Hg

1 atmosphere = 101.3 kPa

1 atmosphere = 14.7 lb/in2

Units of Volume:

1 liter (L) = 1 cubic decimeter (dm3)

1 milliliter (mL) = 1 cubic centimeter (cm3)

Temperature Conversions:

°F = (9/5)°C + 32

°C = (5/9)(°F – 32)

K (Kelvins) = °C + 273

°C = K -273

Gas Pressure

Gas pressure- the pressure exerted by a gas on an object.

This pressure is exerted along the total surface area of

the object.

Pressure=Force/Area

Units of Pressure and Conversions

1 atm=101.3 kPa=760 Torr= 760 mm Hg

Some other important definitions

Boiling Point- the temperature of a substance that is

reached when the vapor pressure of that substance is

greater than or equal to the atmospheric pressure.

Atmospheric Pressure-the pressure exerted by the gas

molecules in the atmosphere upon any object.

Vapor pressure – the pressure exerted by a gas above a

liquid in a sealed container

Effect of Pressure on Boiling Point

An Early

Barometer

The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

• Gases assume the volume and shape of their

containers.

• Gases are the most compressible state of matter.

• Gases will mix evenly and completely when

confined to the same container.

• Gases have much lower densities than liquids and

solids.

Physical Characteristics of Gases

Compressibility

Compressibility is a measure of how

much the volume of matter

decreases under pressure

Gasses expand to fill their container

Gasses are easily compressed

Compressibility

At RT, the distance between particles

is about 10x the diameter of the

particle

This empty space makes gases good

insulators (example: windows, fluffy coats)

Q: How does the volume of the

particles in a gas compare to the

overall volume of the gas?

The Gas Laws

Boyle’s Law P1V1 = P2V2 assuming constant

temperature and number of moles.

Charles Law V1/T1 = V2/T2 assuming constant pressure

and number of moles.(T must be in K).

Gay Lussac’s Law P1/T1= P2/T2 assuming constant

volume and number of moles.(T must be in K.)

Pressure and Volume

A plot of V versus P

results in a curve.

Pressure and volume are

inversely proportional –

when pressure increases,

volume decreases, and

vice versa

Volume vs. Temperature

Volume and Temperature are directly related – when

temperature increases, volume increases, and vice

versa

Pressure vs. Temperature

Pressure and Temperature are directly related –

when temperature increases, pressure increases

More Gas Laws

The Combined Gas Law P1V1/T1 = P2V2/T2 assuming

constant number of moles.

The Ideal Gas Law PV = nRT

where n=number of moles and

R is the gas constant

R = 8.31 kPa L/mol K

R = 0.0821atm L/mol K.

Grams A Grams B Moles B Moles A

Volume A if

a GAS

Volume B if

a GAS

Ratio from

Balanced

Equation

Molar mass

From

Periodic

Table

22.4 L/mol IF at STP

OR

PV = nRT if NOT STP

22.4 L/mol IF at STP

OR

PV = nRT if NOT STP

Molar mass

From

Periodic

Table

KNOWN UNKNOWN

Deviations from Ideal Gas Behavior

When does one encounter problems when using the

ideal gas law?

At extremely high pressures.

Low temperatures

Why?

Because our assumptions aren’t true!

Gas molecules have volume

Gas molecules do have attraction to each other

Gas Laws

In the air there are a variety of different gases.

Dalton’s Law

The partial pressures of the component gases add together to

create the total pressure of the mixture.

P1 + P2 + …..Pn = PT

In a sealed vessel of dry, nitrogen has a partial pressure of

79.11 kPa, oxygen has the partial pressure of 21.22 kPa, carbon

dioxide has a partial pressure of 0.04 kPa and argon and others

have a partial pressure of 0.95. What is the total pressure of

dry air?

#6 Dalton’s Law …. And wet gasses?

•Dalton’s Law is particularly useful in

calculating the pressure of gases

collected over water.

Collecting a gas over water –

many gas-collecting experiments

involve this.

Phase Changes

Courtesy www.lab-initio.com

A phase is a homogeneous part of the system in contact with

other parts of the system but separated from them by a well-

defined boundary.

2 Phases

Solid phase - ice

Liquid phase - water

11.1

Intermolecular Forces

11.2

Intermolecular forces are attractive forces between molecules.

Intramolecular forces hold atoms together in a molecule.

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)

Generally,

intermolecular forces

are much weaker

than intramolecular

forces.

“Measure” of intermolecular force

boiling point

melting point

DHvap

DHfus

DHsub

Types of Intermolecular Forces

1. Hydrogen Bond (strongest)

11.2

The hydrogen bond is a special dipole-dipole interaction between the hydrogen

atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT

IS NOT A BOND.

A H … B A H … A or

A & B are N, O, or F

Hydrogen Bond

11.2

Why is the hydrogen bond considered a

“special” dipole-dipole interaction?

Decreasing molar mass

Decreasing boiling point

11.2

Types of Intermolecular Forces

2. Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

11.2

Ion-Dipole Interaction

11.2

Types of Intermolecular Forces

3. Dipole-Dipole Forces

Attractive forces between polar molecules

Orientation of Polar Molecules in a Solid

11.2

Types of Intermolecular Forces

4. Dispersion Forces – van der Walls forces/London forces (weakest)

Attractive forces that arise as a result of temporary dipoles induced in

atoms or molecules

11.2

ion-induced dipole interaction

dipole-induced dipole interaction

Intermolecular Forces

4. Dispersion Forces Continued

11.2

Polarizability is the ease with which the electron distribution in the atom or

molecule can be distorted.

Polarizability increases with:

• greater number of electrons

• more diffuse electron cloud

Dispersion forces

usually increase with

molar mass.

S

What type(s) of intermolecular forces exist between each of the following

molecules?

HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces

between HBr molecules.

CH4 CH4 is nonpolar: dispersion forces.

SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces

between SO2 molecules.

11.2

Intermolecular Forces

11.2

Intermolecular forces are attractive forces between molecules.

(Example: water molecule to water molecule)

Intramolecular forces hold atoms together within in a molecule.

(Example: H to O bond within a water molecule).

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)

Generally,

intermolecular

forces are much

weaker than

intramolecular

forces.

“Measure” of intermolecular force

boiling point

melting point

DHvap

DHfus

DHsub

Intermolecular Forces

1. London Forces (a.k.a. Dispersion Forces) Weakest

2. Dipole-Dipole Interactions

3. Ion-Dipole Interactions

-(Salt dissolving in solution; Na+ and Cl- )

4. Hydrogen Bonding (STRONGEST)

London Dispersion Forces: Weakest Occur between every compound and arise from the net attractive forces

amount molecules which is produced from induced charge imbalances

The larger the molecule the greater

it’s Dispersion Forces are.

Animation:

Figure 10-8 Olmsted Williams

Figure 10-9 Olmsted Williams

http://chemmovies.unl.edu/ChemAnime/LO

NDOND/LONDOND.html

Olmsted Williams Fig 10-10 Pg 437

The boiling point of long molecules increase with the length of

the carbon

chain.

How molecular shape affects the strength of the dispersion forces

The shapes of the molecules also matter. Long thin molecules can develop

bigger temporary dipoles due to electron movement than short fat ones

containing the same numbers of electrons.

Butane has a higher boiling point because the dispersion forces are greater.

http://www.chemguide.co.uk/atoms/bonding/vdw.html

Polarizability

11.2

the ease with which the electron distribution in the atom or

molecule can be distorted.

Polarizability increases with:

• greater number of electrons

• more diffuse electron cloud

Dispersion

forces usually

increase with

molar mass.

Is the Molecule Polar?

The more Electronegative atom will pull the electron density of the bond

Closer to itself giving it a partial negative charge leaving the other

Atom with a partially positive charge. This is a dipole moment.

Molecules with 3 Atoms

HCN

Even though the C-O bond is polar, the bonds

cancel each other out because the molecule is

linear the dipole moments are equal and in

opposite directions.Therefore CO2 is non-polar.

The dipole moment between H-C points in

the direction of C. The dipole moment points

between C-N points in the direction of the N.

Therefore the dipole vectors are additive and

HCN is polar

CO2

SO2 is a polar molecule because the S-O

dipole Moments don’t cancel each other out

due to the angle

SO2

CCl4 is non-polar

CHCl3 is polar

Molecules with 4 Atoms

How to Determine if a Molecule

Is Polar

1. Draw Lewis Structure

2. If all of the regions of electron density are

bound to the same thing (CCl4; CO2 ) than the

molecule is non-polar

3. If the regions of electron density are not bound to

the same thing (atom) than the molecule

is polar (HCN; SO2)

10.2

Which of the following molecules are polar (have a

dipole moment)?H2O, CO2, SO2, and CH4

O

dipole moment

polar molecule

S

C O O

no dipole moment

nonpolar molecule

dipole moment

polar molecule

C

H

H

H H

no dipole moment

nonpolar molecule

Dipole-Dipole Forces

Attractive forces between polar molecules

Orientation of Polar Molecules in a Solid

11.2

Animation: http://chemmovies.unl.edu/ChemAnime/DIPOLED/DIPOLED.html

Figure 10-11

Dipole Forces occur between molecules containing a dipole moment.

The positive end of the dipole moment on one mole is attracted to the

Negative end of the dipole moment on a nearby molecule.

2-methyl propane

(left) and acetone (right)

Both compounds are about

Equal in size and shape

Olmsted Williams

Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

11.2

Ion-Dipole Interaction

The larger the charge the stronger the force

Fig 10-34

A molecular picture showing the ion-dipole

Interaction that helps a solid ionic crystal dissolve

in water. The arrows indicate ion-dipole interactions.

Olmsted Williams

S

What type(s) of intermolecular forces exist

between each of the following molecules?

HBr HBr is a polar molecule: dipole-dipole forces. There are

also dispersion forces between HBr molecules.

CH4

CH4 is nonpolar: dispersion forces.

SO2 SO2 is a polar molecule: dipole-dipole forces. There are

also dispersion forces between SO2 molecules.

11.2

The Hydrogen Bond

STRONGEST

INTERMOLECULAR

FORCE

http://chemmovies.unl.edu/ChemAnime/HYBOND/HYBONDD.html

Animation

water has

the highest

melting point

water has

the highest

boiling point

water has the

highest heat of

vaporization

water has the

highest heat

of fusion water has the lowest

molar mass

The melting point, boiling point, heat of fusion and heat of

vaporization of water are extremely high and do not fit the

trend of properties relative to molar mass within Group

VIA.

Water exhibits these unusual

properties because of hydrogen

bonding between water

molecules.

A hydrogen bond is an intermolecular bond.

F—H O—H N—H

• A hydrogen bond is formed between

polar molecules that contain hydrogen

covalently bonded to a small, highly

electronegative atom: F, O, N.

it will be attracted to another F, O, or N, on another

molecule.

hydrogen

bond

covalent

bond

covalent

bond

• A dipole-dipole bond bond will be

formed between the two molecules

which is called a hydrogen bond.

13.8

Water in the liquid and solid states exists as groups in

which the water molecules are linked together by

hydrogen bonds.