Chapter 03 The Chemistry of Global Warming

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Free Powerpoint Templates

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The Chemistry of Global

Warming

Chapter 3 Chemistry in Context

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Global Climate Change

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Definition

the accelerated warming of earth's atmosphere that is believed to result from a buildup of one or more greenhouse gases (primarily carbon dioxide,

methane, and nitrous oxide) due to human

activities

=

the increase in average global temperatures

the scientific evidences

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Difference

GLOBAL WARMING

is the increase of the Earth’s average

surface temperature due to a build-up of greenhouse gases in the atmosphere.

CLIMATE CHANGE

is a broader term that refers to long-term

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Effects of Global Warming

Increased Temperature

Habitat Damage and

Species Affected

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Earth’s Energy Balance

Shorter

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Sun’s Energy which Reaches Earth

• Ultraviolet (UV); 8 %

• Visible (vis); 39 %

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Greenhouse Effect; Return of ~81 % of

Re-radiated Energy Back Towards Earth

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Molecular Vibrations: Energy

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Major Greenhouse Gases:

Carbon Dioxide & Water

CO₂ absorption spectrum : strong peaks at 15 um and 4.26 µm (both of which are in the thermal IR but radiation from earth not very strong in 4-5 µm region)

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Enhanced Greenhouse Effect

Increases the average global temperature above the optimal amount due to an energy return greater than

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Gases

Greenhouse Gases

• Carbon dioxide; CO2

• Water; H2O

• CFC’s

• Nitrous Oxide; N₂O

• Methane; CH₄

NOT Greenhouse Gases

• Nitrogen; N₂

• Oxygen; O₂

• Argon; Ar

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3.3

Draw Lewis Structures for:

O₂ CH₄

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-_{+ ½ bonding e}-_]

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

Remember: Resonance, relative lengths and bond order!

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Representations of methane

3.3 Lewis structures

show connectivity

This Lewis structure is drawn in 3-D

Space-filling Charge- density

CH₄ = molecular formula; does not express connectivity

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The

3-D shape

of a molecule affects ability to

absorb IR radiation.

3.3

Valence Shell Electron Pair Repulsion Theory

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3.3 Four electron pairs as far from each other as

possible indicates a tetrahedral arrangement.

A tetrahedral shaped molecule has

bond angles of 109.5o.

Valence Shell Electron Pair Repulsion Theory

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3.3 The legs and

shaft of a music stand

are 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, but

the shape is described only in terms of the atoms

present: water is said to be bent shaped.

The non-bonding electron pairs

take up more space than

bonding pairs, so the H-to-O-to-H bond angle is

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We can use the VSEPR model to allow us to predict the shape of other molecules.

Number of electron pairs

around central atom Shape of molecule Bond angle

4 electron pairs, all bonding:

CH₄, CF₄, CF₃Cl, CF₂Cl₂ tetrahedral 109.5 o

4 electron pairs, three

bonding, one non-bonding:

NH₃, PCl₃ Triangular pyramid about 107 o

4 electron pairs, two

bonding, two non-bonding:

H₂O, H₂S bent about 105

o

Other predictions can be made based on

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3.3

Now look at the central atom of CO₂:

Two groups of four electrons each are associated with the central atom.

The two groups of electrons will be 180o

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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

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3.4

The infrared spectrum for CO₂

As IR radiation is absorbed, the

amount of radiation that

makes it through the

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3.4

The infrared spectrum for CO₂

Wavenumber (cm-1_{) =} _10,000

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3.4

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Free Powerpoint Templates temperature from deuterium content and estimate CO2 concentrations for air bubbles

• Athmospheric CO₂ concentration

Over very long periods of time; CO2 concentration has increased when average global temperature has increased.

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There are

Seasonal

Fluctuations

in Carbon

Dioxide

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Over very long

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The carbon cycle

3.7

A mole of atoms of any element has a

mass (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.

Avogadro’s number is

6.022 x 1023

Atomic number

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The carbon cycle

3.7

6.022 x 1023

Atomic number

Mass number One mole of carbon has a

mass of 12.01 grams;

1 mol C = 12.01 g

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

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moles _molecules grams use_molar

mass

use

Avogadro’s number

Keep these relationships in mind:

3.7

Remember – the critical link between moles

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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

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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?

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Deforestation contributes another 1-2 bmt/year

3.5

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Amplification of Greenhouse Effect:

Global Warming:

What we know

1. CO₂ contributes to an elevated global temperature.

2. The concentration of CO₂in the atmosphere has been increasing over the past century.

3. The increase of atmospheric CO₂is a consequence of human activity.

4. Average global temperature has increased over the past century.

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What might be true:

1. CO₂and other gases generated by human activity are responsible for the temperature increase.

2. The average global temperature will

continue to rise as emissions of anthropogenic greenhouse gases increase.

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82% of ice field has been lost since 1912

The snows of Kilimanjaro

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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.

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Kyoto Protocol -

1997 Conference

•Intergovernmental Panel on Climate Change (IPCC) certified the scientific basis of the

greenhouse 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, HFC’s, PFC’s, and SF₆)

•Trading of emission credits allowed.

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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.

Notable country who has not signed

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