Green Chemistry

AS Level

The Greenhouse Effect – Global warming

Learning Objectives

• Explain that infrared radiation by C=O, O-H and C-H bonds in CO2, H2O and CH4, and this contributes to global warming.

• Explain that the greenhouse effect of a given gas is dependent both on its atmospheric concentration and its ability to absorb infrared radiation.

The greenhouse effect isn’t all bad

• Without greenhouse gases our planet would be covered in ice with an average temperature 35oC less than present.

• The temperature of our planet has more to do with the greenhouse effect than with our proximity to the sun!

• The Earth receives most of its energy in the form of electromagnetic radiation from the Sun.

• Most from visible, some from UV and IR regions.

• The incoming radiation is relatively unaffected by the gases in the Earth’s atmosphere.

• Most IR radiation goes back into space, however certain gases absorb this radiation, some is re-emitted back towards the Earth.

• This traps the heat in the lower atmosphere.

So what’s the problem?The greenhouse effect is a natural process,

keeping our planet at a temperature capable of supporting life. Human activity is producing more greenhouse gases, which threaten to upset this fine natural balance, resulting in global warming.

The greenhouse effect creates an equilibrium.

The atmospheric gases absorb energy at the same rate it radiates it, thus maintaining a steady temperature.

Greenhouse effect definition:

• The greenhouse effect is the process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface.

Greenhouse gases• Water vapour – from evaporation of

lakes and oceans. Most abundant.

Greenhouse gases• Carbon dioxide – produced by volcanic

eruptions, respiration of animals and burning or organic matter (plants).

Greenhouse gases• Methane – emitted during the production of

fossil fuels, rotting waste in landfill sites and released from certain animals (cows). Least amount but greatest contributor.

Methane bubbles in a frozen pond

• Clathrates – contain 3000x as much methane as atmosphere, if released this would have a huge effect on greenhouse gases. These are blamed for the Bermuda Triangle.

There is some speculation that these have added to global warming, but there is

no concrete proof.

How do gases absorb radiation?

• When it absorbs IR radiation it vibrates.

• Eventually it emits this vibrating energy as radiation.

• This can then be absorbed by another greenhouse gas molecule or the Earth’s surface.

• In H2O = O-H bonds absorb IR• In CH4 = C-H bonds absorb IR

• What shape is a CO2 molecule?

Global warming potential (GWP)

• The ability of a trace gas to cause global warming is described by its GWP.

• GWP is related to the lifetime of a gas in the atmosphere as well as the ability of a gas to absorb IR radiation.

• Since banning use of CFC’s their effect is diminishing.

Questions

1. Name the three greenhouse gases2. Outline the molecular processes

that enable heat to be kept close to the Earth.

3. What factors contribute to a gas’s contribution to global warming?

Climate change

Learning Objectives

• Explain the importance of controlling global warming caused by atmospheric increases in greenhouse gases.

• Outline the role played by chemists through the provision of scientific evidence that global warming is taking place.

• Understand the role of chemists in monitoring progress of initiatives such a Kyoto protocol.

Global warmingGlobal warming can be seen in:• In the Arctic, ice and permafrost

disappearing• In the Antarctic, ice sheets melting

into the oceans• Tropical areas experiencing more

frequent and destructive storms and floods

• In Europe, glaciers are disappearing and there have been extreme heat waves.

Reducing Greenhouse Emissions

• Earth Summit in 1992 – international agreement that climate change must be prevented, but there was little action.

• Kyoto Protocol – 0ver 100 countries. Countries must reduce emissions of six greenhouse gases by 5% by 2012.

• USA – biggest emitter (25% of global emissions) – refused to sign.

• Carbon emissions need to be reduced by 70-80%, even with new wind turbines, etc.

EU strategy for the future

2007 binding targets, by 2020:• At least 20% of energy used in the EU will

come from renewable sources.• Al least 10% of fuels used in transport will

be biofuels.• EU greenhouse gas emissions will be

reduced by 20% below 1990 levels.• Reduce greenhouse gases by 30%.

Climate Change Bill – By 2050 C emissions cut by 60%.

Governments listen to the scientists

• Politicians are now slowly believing what scientists have been saying for years “Human activity is contributing to global warming”.

• Politicians are now looking for measures to reduce carbon emissions.

• Kyoto Protocol and EU initiatives prove governments are listening.

Questions1. List three consequences of global

warming for the Earth.2. Petrol contains a mixture of

hydrocarbons, including isomers of C8H18.

a) Write a balanced equation for the complete combustion of C8H18 (assume petrol contains just this).

b) Calculate the reduction in CO2 emission from a car per km in 2012 (130g CO2 per km) compared with 2005 (162g CO2 per km) by volume.