TYpes of Chemical Reactions Part 3

Types of REactions Synthesis Reactions Decomposition Reactions Single Displacement Reactions Double Displacement Reactions Combustion Corrosion

combustion Combustion is the chemical reaction in which fuel “burns” or reacts quickly with oxygen The products of this reaction are usually an oxide and energy Sunrise Propane Explosion Toronto 2008

Hydrocarbons Hydrocarbons (HC) are a group of compounds that only contain the elements carbon and hydrogen Example: Propane, C 3 H 8 HC originate from fossil fuels The combustion of HCs power cars & buses, warm homes, generate electricity & light candles

Complete combustion of Hydrocarbons Products of HC combustion can vary - depend on availability of oxygen Plentiful oxygen = complete combustion Complete combustion of HC: hydrocarbon + oxygen → CO 2 + H 2 O + energy CO 2 is an important green house gas - more in climate change unit!

complete combustion of hydrocarbons The balanced chemical equation for the complete combustion of hydrocarbons can be represented by the general equation: C x H y + O 2 → CO 2 + H 2 O + energy During complete combustion, fuel burns clean with no sooty residue

Incomplete combustion of hydrocarbons If oxygen supply is limited, incomplete combustion may occur Results in release of carbon monoxide gas and carbon (soot) in addition to carbon dioxide and water An orange flickering flame indicates incomplete combustion

Carbon Monoxide (CO) Carbon monoxide is a colourless, odorless gas Highly toxic Symptoms of poisoning - headaches, dizziness, nausea, respiratory problems Cause of many deaths - incomplete combustion in confined space Carbon monoxide detectors!

soot Made up of particles of carbon Causes pollution and wastes energy Common in older vehicles with poorly maintained engines Common result of forest fires

Other combustion reactions Many substances (besides HC) undergo combustion Elements react with oxygen to form oxides General equation: element + oxygen → oxide + energy Eg. magnesium burns to form magnesium oxide + energy

Corrosion Is the breakdown of metal as a result of chemical reactions with the environment

beneficial corrosion Example: aluminum exposed to air Corrodes to form aluminum oxide - one of the hardest substances known Aluminum oxide tightly coats underlying metal, preventing further corrosion Application - camping pans

rust Familiar reddish-brown flaky material produced when metals containing iron corrode Rust does not stick well to underlying steel Readily flakes away so fresh steel is exposed to further corrosion Continues until steel is completely eaten away!

rust Causes of rust: Oxygen Water Electrolytes - not a cause, but speeds up corrosion once it starts

Preventing corrosion Protective Coatings Cover metal with rust inhibiting paint, chrome or plastic coating Corrosion still possible with chips/scratches Corrosion resistant materials Plastic - Eg. car bumpers Corrosion resistant alloys (blend of metals) - Eg. surgical knee implant

Galvanizing Galvanized steel is steel coated with thin layer of zinc Zinc corrodes before steel Zinc corrodes to form protective oxide layer

Demo of the day! Time for some combustion in action! Combustion of acetylene 2C 2 H 2 (g) + 5O 2 (g) → 4CO 2 (g) + 2H 2 O (g)