Greenhouse+effect

=** ﻿ Green House Effect**=
 * Chemistry SL**
 * Sam Tsai**

The Sun is the major source of external energy on Earth. The Sun emits energy as electromagnetic radiation; energy that does not need to travel through a medium; it can travel through the vacuum of space.

The Sun's radiation enters the Earth's atmosphere as shorter wavelength UV and visible light. some of this radiation is re-radiated back into space and some is absorbed by gases in the atmosphere. most passes through the atmosphere, however, and warms the surface of the Earth. The warm Earth surface then radiates some of this energy as longer Wavelength infrared radiation.

Much of this longer wavelength energy is too long to pass through the Earth's atmosphere

The longer wavelength energy is absorbed by molecules such as carbon dioxide (CO 2 ), methane (CH 4 ) etc.

a covalent bond is like a spring in that it vibrates at a natural frequency. when infrared radiation has the same frequency as a covalent bond, the molecule absorbs the radiation and the bonds increase their vibration.
 * Reason:**

This makes the air warmer causing the air itself to radiate heat in turn. some of this radiation is re-radiated back to the Earth's surface and some is re-radiated back to the Earth's surface and some is re-radiated back into space. This natural process is called the green house effect.
 * Green House Gases**

Not all kinds of gas are equally effective in absorbing infrared. The ability to absorb infrared depends on the change in dipole moment that occurs as a molecule vibrates. Non-polar diatomic molcules with the same atoms, such as N2 and O2 are not green house gases as they do not absorb radiation. **The ability of a gas to absorb infrared is quantified by what is know as the greenhouse factor**, which compares the ability of a substance to absorb infrared to CO 2 .


 * Green House Gas ||  Main Source  ||  Greenhouse Factor  ||  Overall contribution to increased global warming (%)  ||
 * Water H 2 O ||  Evaporation of oceans and lakes  ||  0.1  ||  -  ||
 * Carbon Dioxide CO 2  ||  Increased levels owing to combustion of fossil fuels and biomass  ||  1  ||  50  ||
 * Methane CH 4 ||  Anaerobic decay of organic matter, increased levels caused by intensive farming  ||  30  ||  18  ||
 * CFCs ||  Refrigerants, pollutants, foaming agents, solvents  ||  Around 20 000  ||  14  ||
 * Ozone O 3 ||  Secondary pollutants in photochemical smog  ||  2000  ||  12  ||
 * Di-nitrogen Oxide N 2 O ||  Increased levels owing to artificial fertilizers and combustion of biomass  ||  160  ||  6  ||
 * Sulfur Hexafluoride (SF 6 ) ||  Used as an insulator in the electrical industry  ||  22000  ||  0.05  ||




 * Positive and Negative Influences on the atmosphere of increasing amount of green house effect:**

Positive: - Lower heating bills during the winter - Longer growing season

Negative: - Air conditioning usage is higher during the summer and thus more CFCs needed - change in precipitation patterns and global temperature - melting of the polar ice caps and glaciers - rising sea levels lead to floods in some areas. - changes in the distribution of pests and disease-carrying organisms - changes in biodiversity

Pictures & Reference:

Green House effect diagram. Retrieved: 4/10/10 [] Cows contribute to green house effect. Retrieved: 4/10/10 [] About.com Guide. What are Greenhouse Gases. Retrieved: 4/10/10  []  Umich.EDU. Greenhouse Gases. retrieved: 5/10/10 [] Catrin Brown. Mike Ford. Standard level chemistry developed specifically for the IB Diploma. First published 2008. Person Education. Environmental Chemistry. N.A. Enviornmental Chemistry (Chemistry Notes provided.)