Chapter 3 - akugakbutuheksis

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Transcript Chapter 3 - akugakbutuheksis

The Chemistry of Global
Warming
Chapter 3 Chemistry in Context
Catatan: Diambil dari berbagai sumber
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Global Climate Change
• Mean annual global temperature,1960–2003
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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
What are ?
the
effects
the role of
chemistry in
understanding
role of human
activities
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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
changes in climate,
including average
temperature and
precipitation.
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Effects of Global Warming
Rising Sea Level
Increased Temperature
Habitat Damage and
Species Affected
Changes in Water Supply
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Venus has an average temperature of
450°C; It’s atmosphere contains 96 % CO2
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Earth’s Energy Balance
Shorter
wavelengths are
yellow; longer
are red
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Sun’s Energy which Reaches Earth
• Ultraviolet (UV);
• Visible (vis);
• Infrared (IR);
8%
39 %
53 %
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Greenhouse Effect; Return of ~81 % of Reradiated Energy Back Towards Earth
Chemistry; The Science
in Context; by Thomas R
Gilbert,Rein V. Kirss, and
Geoffrey Davies, Norton
Publishers, 2004, p335
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Molecular Vibrations: Energy
Absorption by Greenhouse Gases
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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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CO2 absorbs
½ 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 than
81%.
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Gases
Greenhouse Gases
•
•
•
•
•
NOT Greenhouse
Gases
Carbon dioxide; CO2
Water; H2O
CFC’s
Nitrous Oxide; N2O
Methane; CH4
• Nitrogen; N2
• Oxygen; O2
• Argon; Ar
why ?
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Review: How to draw Lewis structures
1. Determine the sum of valence electrons Draw Lewis Structures for:
CH4
2. Use a pair of electrons to form a bond O2
between each pair of bonded atoms
3. Arrange the remaining electrons to
satisfy octet rule (duet rule for H)
4. Assign formal charges
SO2
C2H4
SO42-
CO
H2SO4
N2--------------------------------NO3O3
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!
3.3
Representations of methane
CH4 = molecular formula; does not express connectivity
Structural formulas show how atoms are connected:
Lewis structures
show connectivity
This Lewis
structure is
drawn in 3-D
Space-filling
Chargedensity
3.3
The 3-D shape of a molecule affects ability to
absorb IR radiation.
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
3.3
Valence Shell Electron Pair Repulsion Theory
Consider methane (CH4), where the central carbon
atom has 4 electron pairs around it:
Four electron pairs as far from each other as
possible indicates a tetrahedral arrangement.
A tetrahedral
shaped
molecule has
bond angles
of 109.5o.
3.3
Valence Shell Electron Pair Repulsion Theory
The legs and
shaft of a
music stand
are like the
bonds of a
tetrahedral
molecule.
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 nonbonding
electron pairs
take up more
space than
bonding pairs,
so the H-to-Oto-H bond
angle is
compressed.
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.
3.3
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
109.5o
Triangular pyramid
about 107o
bent
about 105o
4 electron pairs, three
bonding, one non-bonding:
NH3, PCl3
4 electron pairs, two
bonding, two non-bonding:
H2O, H2S
Other predictions can be made based on
other electron pair arrangements .
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
from each other: the
CO2 molecule is linear.
3.3
Molecular geometry and absorption of IR radiation
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
The infrared spectrum for CO2
As IR
radiation is
absorbed, the
amount of
radiation that
makes it
through the
sample is
reduced
3.4
The infrared spectrum for CO2
Wavenumber (cm-1) = 10,000
wavelength (mm)
3.4
Molecular response to different types of radiation
3.4
How to study
global warming
• Ice core data
Ice Core data is used to infer
temperature from deuterium content
and estimate CO2 concentrations for
air bubbles
• Athmospheric
concentration
CO2
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
Concentration
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Over very long
periods of time; CO2
concentration has
increased when
average global
temperature has
increased.
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Carbon Dioxide Concentration has
Increased since 1870
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Ice core data and CO2 concentration
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Carbon Dioxide Cycle
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Fig.03.20
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Mole: SI definition: the number
equal to the number of carbon atoms
in exactly 12 g of pure C-12.
Atomic number
Mass number
Avogadro’s
number is
6.022 x 1023
A mole of atoms of any element has a
mass (in grams) equal to the atomic
mass of the element
amu.cycle
The in
carbon
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?
mol C = 3.0 mol C
36.03 g C x 112.01
gC
The carbon cycle
3.7
Keep these relationships in mind:
grams
use
molar
mass
moles
use
Avogadro’s
number
molecules
Remember – the critical link between moles
and grams of a substance is the molar mass.
3.7
Chemistry behind Global Warming
Calculate the number of molecules in 4.53 moles of
carbon dioxide. 2.73 x 10 24
Caffeine has the formula C8H10N4O2. How many
molecules are in 10.0 g of pure caffeine? (The molar
mass of C8H10N4O2 is 194 g/mol.) 3.1 x 1022
How many grams of CO2 are needed to be sure of
having exactly 3.0 x 102 mol of CO2? 1.3 x 104 g
How many atoms are in 0.35 mol of CO2?
6.3 x 1023
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
CO2 emission sources from fossil fuel consumption
Deforestation contributes another 1-2 bmt/year
3.5
Amplification of Greenhouse Effect:
Global Warming:
What we know
1. CO2 contributes 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 increased
over the past century.
3.2
What might be true:
1. CO2 and 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.
3.9
The snows of Kilimanjaro
82% of ice field has
been lost since 1912
3.9
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
3.9
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.
3.11
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
3.11