Chapter 7 States of Matter (gases, liquids and solids)

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Figure 1.2 (a) A solid has a definite shape and a definite volume. (b) A liquid has an indefinite shape -it takes the shape of its container - a definite volume. (c) A gas has an indefinite shape and an indefinite

volume.

solid liquid gas

• A solid has a definite shape and a definite volume• A liquid has no definite shape (it takes the shape of its container) but a definite volume• A gas has no definite shape or volume

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• In a gas, the particles are in constant random motion, each particle being independent of the others present.

• The particles in a liquid, though still close together, freely slide over one another.

• In a solid, the particles (atoms, molecules, or ions) are close together and vibrate about fixed sites.

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1. Matter is composed of tiny particles (atoms, molecules, or ions) that have definite and characteristic sizes that do not change.

Kinetic Molecular Theory of Matter

2. The particles are in constant random motion and therefore possess kinetic energy. Kinetic energy – energy that matter

possesses because of particle motion.

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3. The particles interact with one another through attractions and repulsions and therefore possess potential energy. Potential energy – stored energy that matter

possesses as a result of its position, condition, and/or composition.

4. The kinetic energy (velocity) of the particles increases as the temperature is increased.

5. The particles in a system transfer energy to each other through elastic collisions.

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Solid: High densitySmall compressibilityVery small thermal expansion

Liquid:High densitySmall compressibilitySmall thermal expansion

Gas: Low densityLarge compressibilityModerate thermal expansion

Fig. 7.5

Pages 165 - 166

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I. Properties of gases A. Pressure

P = force/areaUsually measured by height of Hg

(mercury)

1 atmosphere pressure = 1 atm = 760 mm Hg

=760 torr

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Figure 6.3

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Page 178 Chemical Connections

Systolic pressure Diastolic pressureMeasure of bloodpressure

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Systole is the contraction of heart chambers, driving blood out of the chambers.

Diastole is the period of time when the heart relaxes after contraction.

Systolic pressure - the highest arterial pressure during each heart beat.

Diastolic pressure - the lowest arterial pressure between heart beats

Normal range:

Normal range:

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B. Volume, L C. Temperature, K 273K = 0oC K = oC + 273

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D. The Gas Laws

a) Boyle’s law

or PV = constant or P1V1 = P2V2

Constant temperature

pV

1

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b) Charles law

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Figure 7.12 Data illustrating the direct proportionality associated with Charles's law.

2

2

1

1

T

V

T

V

Constant pressure

T

Vconstant oror

TV

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c) The Combined Gas Law

Boyle's law: P1V1 = P2V2 pV

1

Charles law: TVT

V

T

V

2

2

1

1

Combined gas law:

P

TV or

T

PVconstant

2

22

1

11

T

VP

T

VP Combined gas law

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Example (1) A gas occupies 3L at 2 atm. What would be the pressure if the volume was 6L at the same temperature?

Example (2) A gas occupies 2.0 L at 200K and 1.0 atm pressure. What temperature would it be if the volume was 3.0L and the pressure was 380 torr?

2

22

1

11

T

VP

T

VP

14

nVP

TV ,

(n = number of moles)

P

nTRV

P

nTV

PV = nRT Ideal gas law

R = gas constant = 0.0821 Kmol

Latm

Example 2.00 mol of CH4 occupies 16.4 L at 200K. What is the pressure?

d) The ideal Gas law

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g) Dalton's law of partial pressure Consider a mixture of two gases A and B at V, T.

V

RTn

V

RTn

V

RTnnP BABA

T

)(

= PA + PB

Example: A 10 L container contains 2.0 mol O2 and 4.0 N2 at 300K. Find PO2, PN2 and PT.

Total pressure

partial pressure of A partial pressure of B

PV = nRTV

nRTP

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PT = P1 + P2 + P3 + . . .In general

Example:Example: to a tank containing N2 at 2.5 atm and O2 at 1.5 atm

we add an unknown quantity of CO2 until the total pressure

in the tank is 5.2 atm. What is the partial pressure of CO2?

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Figure 7.15 There are six changes of state possible for substances.

E. Changes of state

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1. Evaporation and condensation

H2O

evaporation

H2O

condensation

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H2O

2. Vapor pressure (v.p.) of liquids

evaporation

condensation

rate (evaporation) = rate (condensation)

liquid vapor

State of equilibrium (Saturation)

Vapor pressure = partial pressure exerted by the vapor above the liquid at saturation at a given temperature

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Evaporation of a Liquid in a Closed Container

Figure 7.17

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Vapor pressure increases with temperatureV

apor

pre

ssur

e

Temperature

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3. Boiling – evaporation occurs anywhere in the liquid

Normal boiling point – T at which v.p. of the liquid = 1 atm.

or boiling T under 1 atm

atmAt 100oC, v.p. of water = 1 atm

v.p.

(w

ater

)

T 100oC

1 atm

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T

Heating time

100oC

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4. Conditions that affect boiling pointa) External Pressure:

Boiling point increasesas Pext increases

b) Attractive forces between molecules:

The stronger the attractive forces, the higher the

boiling point

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G. Intermolecular forcesa) Dipole-dipole interaction H Cl H Cl

+ - + -

H Cl H Cl H Cl H Cl

Cl H Cl H Cl H Cl H

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b) London dispersion forces

Nonpolar molecules such as H2 can develop instantaneous dipoles and induced dipoles. The attractions between such dipoles, even though they are transitory, create London forces.

Induced-induced dipole forces

London force increases with size of the molecule

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CH3CH2CH2CH3 CH3-C-CH3

O-

+Butane

(bp 0.5°C)Acetone(bp 58°C)

Consider

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b) Hydrogen bonds

H F H O H N

Example: H2O

H O

H

H

O

H

- +

hydrogenbond

hydrogenbond

- +

(a) (b) (c)

figure 6.9

Structuralformulas

ball and stickmodels

electron densitymodels

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H2OH O

H

H

OH

H O

HH

O H

H

O H

H

OH

H C

H

H

O H

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If there were no hydrogen bonding between water molecules, the boiling point of water would be approximately - 80C.

oC

oC

oC

oC

oC

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cannot H-bond with another

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For compounds of similar dipole moment, the larger the MW, the higher the boiling point.

For compounds of similar MW, the larger the dipole moment, the higher the boiling point.

In general

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Boiling point of compounds that can form H-bonds are relatively high.

H-bond > dipole-dipole forces > London forces

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Circle those compounds below in which the molecules are capable of forming hydrogen bonds between themselves.

NH3 NF3 HF

CO2 H C

H

O H C

H

O

H

H

In each pair below, circle the compound with the higher boiling point:

(1) O2 or Cl2 (2) H2O or H2S

(3) HBr or CF436