1. Redox and Combustion

2. Redox and Combustion: At the conclusion of our time together, you should be able to: 1.Identify a basic combustion reaction 2.Balance a combustion reaction 3.Show the change in oxidation numbers for a combustion reaction

3. 5. Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark) 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

4. Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O In general: C x H y + O 2  CO 2 + H 2 O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by- products like carbon monoxide) Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by- products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 ) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 )

5. Combustion Reactions Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

6. Combustion of Pentane: Predict the products and balance the reaction: Predict the products and balance the reaction: C 5 H 12 + O 2  CO 2 + H 2 O 568

7. Predict the products and balance the reaction: Predict the products and balance the reaction: C 3 H 7 OH + O 2  CO 2 + H 2 O Combustion of Propanol 2689

8. Combustion of Methane and Redox CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + H 2 O Show the change in oxidation numbers: Show the change in oxidation numbers: C -4  C +4 C -4  C +4 Each carbon loses 8 electrons – oxidation, reducing agent O  O 2- O  O 2- Each oxygen gains 2 electrons – reduction, oxidizing agent 122

9. Redox and Combustion: Let’s see if you can: 1.Identify a basic combustion reaction 2.Show the change in oxidation numbers for a combustion reaction

10. Practice Predict the products and balance the reaction of hexene burning in air: C 6 H 12 + O 2  C 6 H 12 + O 2  CO 2 + H 2 O Show the change in oxidation numbers: Show the change in oxidation numbers: C -2  C +4 C -2  C +4 Each carbon loses 6 electrons – oxidation, reducing agent O  O 2- O  O 2- Each oxygen gains 2 electrons – reduction, oxidizing agent 6 69