hydrocarbon + oxygen  carbon dioxide + water + energy Types of Chemical Reactions: Combustion Reactions 6.9 Combustion reactions occur when a substance reacts with oxygen. The products are usually an oxide and energy.   combustion complete combustion incomplete combustion Complete Combustion of Hydrocarbons When hydrocarbons undergo complete combustion, the general word equation is  hydrocarbon + oxygen  carbon dioxide + water + energy CxHy + O2  CO2 + H2O + energy   The complete combustion of butane (C4H10) would be   C4H10(g) + O2(g)  CO2(g) + H2O(g) + energy CAN YOU BALANCE THIS?

6.9 Types of Chemical Reactions: Combustion Reactions   Incomplete Combustion of Hydrocarbons When the oxygen supply is limited, hydrocarbons undergo incomplete combustion. This produces carbon (soot) and carbon monoxide gas, in addition to carbon dioxide and water. The incomplete combustion of butane (C4H10) would be  C4H10(g) + O2(g)  CO2(g) + H2O(g) + CO(g) + C(s) + energy  CAN YOU BALANCE THIS REACTION? Other Combustion Reactions Other examples of combustion include  4 Al(s) + 3 O2(g)  2 Al2O3(s) + energy  2 H2(g) + O2(g)  2 H2O(g) + energy combustion complete combustion incomplete combustion Notice, other combustions have the equation A + O  AO + energy What type of reaction is this?

Corrosion 6.10 Corrosion is the breakdown of a metal as it reacts with chemicals in the environment.   Beneficial Corrosion Sometimes corrosion of some metals forms a tough protective layer that prevents further corrosion. For example,  4 Al(s) + 3 O2(g) 2 Al2O3(s) + energy Copper also forms a protective coating when it corrodes? DO YOU KNOW WHAT COLOUR THIS COATING IS? corrosion glavanized steel electrolytes

RUSTING The reddy-brown flaky material that is produced when metals containing iron corrode. It does not stick well, the way some other protective coatings do, so the metal wears away. This process continues until the metal is completely corroded or ‘eaten away’. Rusting is caused or accelerated by exposure to oxygen exposure to water exposure to electrolytes Methods of preventing corrosion include protective coatings (paint, plastic coatings, chrome) corrosion-resistant materials (stainless steel, plastics) galvanizing (galvanized steel) (a protective Zn coating)

QUESTIONS FOR REFLECTION The corrosion of which metallic objects should cause the public great concern for their safety? Why are our food cans made out of aluminum? Can you think of a common household feature (outdoor) that is galvanized? Why should a car owner care if her car paint gets scratched? Should she care more or less if she lives in the Kalahari than if she lives in Mumbai? Why is it important for a car to be clean and dry before being treating with a rust-proofing product? How could your knowledge about corrosion impact your decision to get a tongue piercing or not? Can you think of an important building made of metal? Why hasn’t it rusted away yet?