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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.
Valence Shell Electron Pair Repulsion Theory
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.
Valence Shell Electron Pair Repulsion Theory
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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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