chapter 3-the chemistry of global warming-indriana

8/10/2019 Chapter 3-The Chemistry of Global Warming-Indriana

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The Chemistry of Global

Warming

Chapter 3 Chemistry in Context
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Definition

the accelerated warming of earth's atmospherethat is believed to result from a buildup of one ormore greenhouse gases (primarily carbon dioxide,methane, and nitrous oxide) due to humanactivities

=

the increase in average global temperatures

the scientific

evidences

the role ofchemistry in

understanding

the

effects

role of human

activities

What are ?
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Difference

GLOBAL WARMING

is the increase of the

Earths average

surface temperaturedue to a build-up of

greenhouse gases in

the atmosphere.

CLIMATE CHANGE

is a broader term that

refers to long-term

changes in climate,including average

temperature and

precipitation.


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Effects of Global Warming

Increased Temperature

Habitat Damage andSpecies Affected Changes in Water Supply

Rising Sea Level


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Venus has an average temperature of

450C; Its atmosphere contains 96 % CO2


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Earths Energy Balance

Shorter

wavelengths are

yellow; longerare red


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Suns Energy which Reaches Earth

Ultraviolet (UV); 8 %

Visible (vis); 39 %

Infrared (IR); 53 %


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Greenhouse Effect; Return of ~81 % of Re-

radiated Energy Back Towards Earth

Chemistry; The Science

in Context; by Thomas R

Gilbert,Rein V. Kirss, and

Geoffrey Davies, NortonPublishers, 2004, p335


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Molecular Vibrations: Energy

Absorption by Greenhouse Gases


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Major Greenhouse Gases:

Carbon Dioxide & Water

CO2absorption spectrum : strong peaks at 15 um and 4.26

m (both of which are in the thermal IR but radiation from

earth not very strong in 4-5 m region)

CO2absorbs about the radiation in the 14-16 um region


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Enhanced Greenhouse Effect

Increases the average global temperature above the

optimal amount due to an energy return greater than81%.


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Gases

Greenhouse Gases

Carbon dioxide; CO2

Water; H2O CFCs

Nitrous Oxide; N2O

Methane; CH4

NOT GreenhouseGases

Nitrogen; N2 Oxygen; O2 Argon; Ar

why ?


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3.3

Draw Lewis Structures for:

O2 CH4

SO2 C2H4

SO42- CO

H2SO4 N2----------------------------------

NO3- O3

Review: How to draw Lewis structures

2. Use a pair of electrons to form a bond

between each pair of bonded atoms

3. Arrange the remaining electrons to

satisfy octet rule (duet rule for H)

4. Assign formal charges

Formal charge = # of v.e.[# of non-bonding e-+ bonding e-]

or, F.C. = # of v.e.[# of bonds to the atom + # non-bonding e-]

Remember: Resonance, relative lengths and bond order!

1. Determine the sum of valence electrons


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Representations of methane

3.3

Lewis structures

show connectivity

This Lewis

structure isdrawn in 3-D

Space-filling Charge-

density

CH4= molecular formula; does not express connectivity

Structural formulas show how atoms are connected:


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The 3-D shapeof a molecule affects ability to

absorb IR radiation.

3.3

Valence Shell Electron Pair Repulsion Theory

Assumes that the most stable molecular shape has the

electron pairs surrounding a central atom as far away

from one another as possible


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3.3

Four electron pairs as far from each other as

possible indicates a tetrahedral arrangement.

A tetrahedral

shapedmolecule has

bond angles

of 109.5o.


Consider methane (CH4), where the central carbon

atom has 4 electron pairs around it:


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3.3

The legs and

shaft of a

music standare like the

bonds of a

tetrahedral

molecule.



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3.3

The central atom (O) in H2O also has four

electron pairs around it,

but unlike methane, two electron pairs are

bonding and two are non-bonding.

The electron pairs are tetrahedral arranged, butthe shape is described only in terms of the atoms

present: water is said to be bent shaped.

The non-

bonding

electron pairstake up more

space than

bonding pairs,

so the H-to-O-

to-H bondangle is

compressed.


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We can use the VSEPR model to allow us to

predict the shape of other molecules.

Number of electron pairsaround central atom

Shape of molecule Bondangle

4 electron pairs, all bonding:

CH4, CF4, CF3Cl, CF2Cl2

tetrahedral 109.5o

4 electron pairs, three

bonding, one non-bonding:

NH3, PCl3

Triangular pyramid about 107o

4 electron pairs, twobonding, two non-bonding:

H2O, H2S

bent about 105o

Other predictions can be made based on

other electron pair arrangements . 3.3


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3.3

Now look at the central atom of CO2:

Two groups of four

electrons each are

associated with thecentral atom.

The two groups of

electrons will be 180o

from each other: theCO2molecule is linear.


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Molecular vibrations in CO2. Each spring represents a C=O

bond.

(a) = no net change in dipole - no IR absorption.

(b, c, d)= see a net change in dipole (charge distribution), so

these account for IR absorption

3.4

Molecular geometry and absorption of IR radiation


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3.4

The infrared spectrum for CO2

As IR

radiation is

absorbed, the

amount ofradiation that

makes it

through the

sample is

reduced


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3.4

The infrared spectrum for CO2

Wavenumber (cm-1) = 10,000wavelength (m)


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3.4

Molecular response to different types of radiation


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How to studyglobal warming

Ice core dataIce Core data is used to infer

temperature from deuterium content

and estimate CO2 concentrations for

air bubbles

Athmospheric CO2concentrationOver very long periods of time; CO2

concentration has increased when

average global temperature has

increased.


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There are

SeasonalFluctuations

in CarbonDioxide

Concentration


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Over very long

periods of time; CO2concentration has

increased when

average global

temperature hasincreased.

Carbon Dioxide Concentration has


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Carbon Dioxide Concentration has

Increased since 1870

Ice core data and CO concentration


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Ice core data and CO2concentration


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Carbon Dioxide Cycle


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Fig.03.20


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The carbon cycle

3.7

A mole of atoms of any element has amass (in grams) equal to the atomic

mass of the element in amu.

Mole: SI definition: the number

equal to the number of carbon atoms

in exactly 12 g of pure C-12.

Avogadros

number is6.022 x 1023

Atomic number

Mass number


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The carbon cycle

3.7

6.022 x 1023Atomic number

Mass number One mole of carbon has amass of 12.01 grams;

1 mol C = 12.01 g

If you have 36.03 g of carbon, how many moles is that?

36.03 g C x1 mol C

12.01 g C= 3.0 mol C


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moles moleculesgrams usemolarmass

useAvogadros

number

Keep these relationships in mind:

3.7

Rememberthe critical link between moles

and grams of a substance is the molar mass.


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Chemistry behind Global Warming

Calculate the number of molecules in 4.53 moles of

carbon dioxide.

Caffeine has the formula C8H10N4O2. How many

molecules are in 10.0 g of pure caffeine? (The molarmass of C8H10N4O2is 194 g/mol.)

How many grams of CO2are needed to be sure of

having exactly 3.0 x 102

mol of CO2?

How many atoms are in 0.35 mol of CO2? 6.3 x 1023

1.3 x 104g

3.1 x 1022

2.73 x 10 24


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Chemistry behind Global Warming

Avogadro's number is 6.0 x 1023. If we have a sample

that contains one mole of carbon dioxide, how many

atoms of oxygen are contained in that sample?

12 x 1023


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Deforestation contributes another 1-2 bmt/year

3.5

CO2emission sources from fossil fuel consumption

Amplification of Greenhouse Effect:


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Amplification of Greenhouse Effect:

Global Warming:

What we know1. CO2contributes to an elevated global temperature.

2. The concentration of CO2 in the atmosphere has

been increasing over the past century.3. The increase of atmospheric CO2 is a

consequence of human activity.

4. Average global temperature has increasedover the past century.

3.2


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What might be true:

1. CO2 and other gases generated by human activity are

responsible for the temperature increase.

2. The average global temperature willcontinue to rise as emissions of anthropogenic

greenhouse gases increase.

3.9


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82% of ice field has

been lost since 1912

The snows of Kil imanjaro

3.9


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Intergovernmental Panel on Climate Change (IPCC)

Recognizing the problem of potential global climate change,the World Meteorological Organization (WMO) and the

United Nations Environment Programme (UNEP)

established the Intergovernmental Panel on Climate Change

(IPCC) in 1988. It is open to all members of the UN and

WMO.

3.9


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3.9

K P l


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Kyoto Protocol - 1997 Conference

Intergovernmental Panel on Climate Change

(IPCC) certified the scientific basis of thegreenhouse effect.

Kyoto Protocol established goals to stabilize and

reduce atmospheric greenhouse gases.Emission targets set to reduce emissions of six

greenhouse gases from 1990 levels.

(CO2, CH4, NO, HFCs, PFCs, and SF6)

Trading of emission credits allowed.

3.11


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The Kyoto Protocol, an international and legally binding

agreement to reduce greenhouse gases emissions world wide,

entered into force on 16 February 2005.

Notablecountry

who has

not signed

3.11


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