6.9Types of Chemical Reactions: Combustion Reactions

combustioncomplete combustionincomplete combustion

combustioncomplete combustionincomplete combustion

Combustion reactions occur when a substance reacts with oxygen. The products are usually an oxide and energy.

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?

Complete Combustion of Hydrocarbons

6.9Types of Chemical Reactions: Combustion Reactions

combustioncomplete combustionincomplete combustion

combustioncomplete combustionincomplete combustion

Incomplete Combustion of HydrocarbonsWhen 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 ReactionsOther examples of combustion include

4 Al(s) + 3 O2(g) 2 Al2O3(s) + energy 2 H2(g) + O2(g) 2 H2O(g) + energy

Notice, other combustions have the

equationA + O AO + energy

What type of reaction is this?

6.10Corrosion

corrosionglavanized steelelectrolytes

corrosionglavanized steelelectrolytes

• 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?

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?