Chapter 3 Chemistry in Context
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Transcript of Chapter 3 Chemistry in Context
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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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Definitionthe 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
the role of chemistry in understanding
the effects
role of human activities
What are ?
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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 WarmingIncreased Temperature
Habitat Damage and
Species Affected
Changes in Water Supply
Rising Sea Level
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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); 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, 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)
CO2 absorbs about ½ the radiation in the 14-16 um region
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Enhanced Greenhouse EffectIncreases the average global temperature above the optimal amount due to an energy return greater than
81%.
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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
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- + ½ 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 is drawn 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 shape of 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 shaped
molecule 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 stand are 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, 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 compressed.
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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 109.5o
4 electron pairs, three bonding, one non-bonding:
NH3, PCl3
Triangular pyramid about 107o
4 electron pairs, two bonding, two non-bonding:
H2O, H2Sbent 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 the central atom.
The two groups of electrons will be 180o from each other: theCO2 molecule 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 of
radiation 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 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 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
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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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
Mass number
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The carbon cycle
3.7
6.022 x 1023Atomic 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?
36.03 g C x 1 mol C12.01 g C = 3.0 mol C
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moles moleculesgramsusemolarmass
useAvogadro’s number
Keep these relationships in mind:
3.7
Remember – the 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 molar mass of C8H10N4O2 is 194 g/mol.)
How many grams of CO2 are 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 104 g
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/year3.5
CO2 emission sources from fossil fuel consumption
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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 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
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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 will continue 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 Kilimanjaro
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
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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.
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.
Notable country who has not signed
3.11
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