Environmental problems Friday, 21 September 2018 Environmental problems L.O: To understand the social, economic and environmental impacts of using fuels.

Combustion We burn fossil fuels (coal, oil and natural gas) to get energy for lots of different processes. Power stations burn huge amounts of fossil fuels to make electricity. Cars are also a major culprit in burning fossil fuels.

Combustion Fossil fuels contain carbon and hydrogen. During combustion (when the fuel is burnt), the carbon and hydrogen react with oxygen from the air so that carbon dioxide and water vapour are released into the atmosphere. The carbon and hydrogen are said to be oxidised. Energy (heat) is also released.

Complete or partial combustion? When there's plenty of oxygen, all the fuel burns — this is called complete combustion. When a fuel is completely combusted only carbon dioxide and water are produced. This is the equation for the complete combustion of a hydrocarbon: If there's not enough oxygen, some of the fuel doesn't burn completely — this is called partial combustion. Under these conditions, solid particles (called particulates) of soot (carbon) and unburnt fuel may be released, as well as carbon dioxide and water. Carbon monoxide (a poisonous gas) is also released.

Quick questions Answers Partial combustion Oxygen Carbon dioxide and water (vapour) Solid particles (particulates) of carbon dioxide (soot), unburnt fuel, carbon dioxide (gas) and water. Hydrogen + oxygen  carbon dioxide + water vapour What is it called when a fuel doesn’t burn completely? Plenty of what is needed for a fuel to burn completely? What are the products of complete combustion? What are the products of a fuel not being burned completely? What is the equation for complete combustion of hydrocarbons? Which is best – complete or partial combustion? Why?

Writing equations for combustion H Writing equations for combustion You could also be asked to write an equation for the partial combustion of a fuel. If so, you'll be told in the question what the products of the reaction are and you'll just need to balance the equation. In the exam, you could be asked to write a balanced symbol equation for the complete combustion of a particular fuel. All you have to do is put the chemical formula of your fuel and O2 for oxygen on one side, CO2 for carbon dioxide and H2O for water on the other side and then make sure the equation balances. Example: Q: Write an equation for the complete combustion of propane. A: Propane has the chemical formula C3H8. If you put C3H8 and O2 on one side of the equation and CO2 and H2O on the other side of the equation you get: Balancing the equation gives you: This is the equation for the complete combustion of propane.

Writing equations for combustion – your go! ANSWER THE FOLLOWING QUESTIONS USING THE EXAMPLE IN YOUR BOOK. Write an equation for the complete combustion of methane (C1H4) Write an equation for the complete combustion of ethane (C2H6) ANSWERS C1H4 + 2O2  2H2O + CO2 2C2H6 + 7O2  6H2O + 4CO2 In an exam, you may not be given the number of carbons and hydrogens. In case of this, you need to remember what the 1st 4 are (remember – Men Eat Prawn Butties!)

Other products of combustion… If the fuel contains sulfur impurities, the sulfur will be released as sulfur dioxide when the fuel is burnt. Oxides of nitrogen will also form if the fuel burns at a high temperature. This is because at very high temperatures, nitrogen and oxygen in the air react with one another. Carbon Dioxide OXIDES OF NITROGEN Sulfur Dioxide Water Vapour

Acid Rain Sulfur dioxide is one of the gases that causes acid rain. When the sulfur dioxide mixes with the water in the clouds it forms dilute sulfuric acid. This then falls as acid rain. Oxides of nitrogen cause acid rain by forming dilute nitric acid in clouds. The formation of acid rain.

Acid Rain

Consequences of acid rain Acid rain causes lakes to become acidic and many plants and animals die as a result. Acid rain also kills trees, damages limestone buildings and ruins stone statues Links between acid rain and human health problems have also been suggested.

Acid rain kills trees… This picture is of a forest of which trees have died from acid rain.

Damages stone statues… Such as the one above, which shows corrosion from the acidic rain.

Causes lakes to become acidic… Which can harm plants and animals near and in the lake, such as the fish in the picture above.

Reducing acid rain The benefits of electricity and travel have to be balanced against the environmental impacts. Governments have recognised the importance of this and international agreements have been put in place to reduce emissions of air pollutants such as sulfur dioxide.

Ways of reducing acid rain MAKE NOTES! Ways of reducing acid rain One way to reduce sulfur dioxide emissions is to remove the sulfur from fuels before they're burnt. The problem is, this costs money. Also, removing sulfur from fuels takes more energy. This usually comes from burning more fuel, which releases more of the greenhouse gas carbon dioxide. Nevertheless, petrol and diesel are starting to be replaced by low-sulfur versions. Another way to reduce sulfur dioxide emissions is to remove the sulfur dioxide from waste gases before they are released. Power stations now have Acid Gas Scrubbers to take the harmful gases out before they release their fumes into the atmosphere. The other way of reducing acid rain is simply to reduce our usage of fossil fuels.

Global Warming The level of carbon dioxide in the atmosphere is increasing — because of the large amounts of fossil fuels humans burn. There's a scientific consensus that this extra carbon dioxide has caused the average temperature of the Earth to increase — global warming  Global warming is a type of climate change and causes other types of climate change, e.g. changing rainfall patterns. It could also cause severe flooding due to the polar ice caps melting. Remember – Global warming and climate change are NOT the same thing. Global warming is a type of climate change. Graph showing how the atmospheric concentration of CO2 and the temperature have changed over the last 250 000 years.

Global dimming In the last few years, some scientists have been measuring how much sunlight is reaching the surface of the Earth and comparing it to records from the last 50 years. They have been amazed to find that in some areas nearly 25% less sunlight has been reaching the surface compared to 50 years ago. They have called this global dimming. They think that it is caused by particles of soot and ash that are produced when fossil fuels are burnt. These particles reflect sunlight back into space, or they can help to produce more clouds that reflect the sunlight back into space. However, there are many scientists who don't believe the change is real and blame it on inaccurate recording equipment.

Thick black smoke being released into the air Thick black smoke being released into the air. The particulate carbon in this smoke could contribute to global dimming.