Presentation on theme: "Chapter 4: Reactions and the Environment Unit A: Matter and Chemical Change."— Presentation transcript:
Chapter 4: Reactions and the Environment Unit A: Matter and Chemical Change
4.1 Fossil Fuel Combustion Fossil fuels are energy resources from the decayed remains of ancient plants and animals. Oil and natural gas are fossil fuels. The energy stored in fossil fuels must be transformed in to other forms of energy before it can be used. Combustion, or burning, is the most common way to transform this energy. A combustion reaction involves a fossil fuel reacting rapidly with oxygen to produce carbon dioxide gas (CO 2 ) and water vapour (H 2 O (g) ).
4.1 Fossil Fuel Combustion (continued) If fossil fuels do not burn completely, they undergo a chemical reaction called incomplete combustion. Occurs when there is not enough oxygen available. Complete combustion produces three products: CO 2(g), H 2 O (g), and energy Incomplete combustion produces five products: CO (g), C (s), CO 2(g), H 2 O (g), and energy
4.1 Fossil Fuel Combustion (continued) All of the combustion reactions in our everyday lives release millions of tonnes of carbon dioxide into the atmosphere. Carbon dioxide is important to life on earth. All living creatures, including plants, produce it naturally. All living things produce carbon dioxide, water vapour, and methane. These are natural greenhouse gasses.
4.1 Fossil Fuel Combustion (continued) Scientists are concerned about the current long-term trend toward global warming. Also, a dramatic increase in extreme climatic events: Glaciers melting, sea levels rising, and climate zones shifting. The real threat is the rate at which climate change is occurring. Climates are changing faster than ever before, many species of organisms may not be able to adapt to such fast changes.
4.1 Fossil Fuel Combustion (continued) Human activities add much more than carbon dioxide into the air. These chemicals in the air that cause harm to living things or the environment are called pollutants. Cause problems like asthma, headaches, and irritation of the eyes, nose, and throat. Also, aggravate heart and lung conditions. Air pollutants can combine with each other to produce acid precipitation. The more accurate term for this phenomenon is acid deposition since dry matter, as well as precipitation, causes acids. See Figure 4.3A on Pg 64
4.2 Acid-Base Reactions In a neutralization reaction, an acid and a base react together to form two new chemical compounds: a salt and water. Neutralization reactions occur in the body.
4.2 Acid-Base Reactions (continued) An example of a neutralization reaction in the environment is liming. This is the process of adding natural limestone (calcium carbonate or CaCO 3(s) ) to lake water to neutralize lakes that have been acidified by acid deposition.
4.2 Acid-Base Reactions (continued) Sulfur and nitrogen oxides are responsible for high levels of acid deposition. The best way to reduce acid deposition is to prevent it from forming. Sulfur dioxide is a major by-product of industrial processes and a product of combustion of fossil fuels like natural gas. To reduce sulfur emissions, sulfur should be removed from the fuel before it is burned.
4.2 Acid-Base Reactions (continued) Sweet natural gas is a way to reduce emissions, the sulfur has been removed from sour natural gas before it is sent to consumers. Coal produced in some areas contains sulfur. A device known as a scrubber is installed on the smokestacks of many industrial plants that burn coal in efforts to prevent sulfur emissions. See Figure 4.8
4.3 Corrosion of Iron Corrosion refers to any process that chemically breaks down or degrades metal. Best-known case is the rusting of iron. Most metals will rust, but the corrosion of iron and steel are a serious problem because these metals are widely used. Rusting → Exposed metal → Weakened structure 4Fe (s) + 3O 2(g) → 2Fe 2 O 3(s) Solid iron + oxygen gas → iron (III) oxide
4.4 Solving the Problem of Corrosion Painting over the metal with a protective coating of paint prevents oxygen and water from reaching the surface of the metal. Not permanent, paint chips off and the water and oxygen attack the steel. Galvanization is the process of applying a zinc coating to iron or steel. Immersing the metal in a bath containing molten zinc provides a protective barrier between the metal and the environment. The zinc coating becomes part of the surface of the steel. Sacrificial metal is the third method of protecting iron. See Figure 4.14