Chemical Reactions 5.1Combustion of Hydrocarbons

Last Class Identified and predicted the products of double displacement reactions using our solubility table and what we know about chemical reactions.

Learning Goals We are learning to… – Identify the types of combustion – Identify the products of combustion – Identify the hazards associated with combustion reactions

Combustion Combustion: a chemical process in which a fuel burns in oxygen. Hydrocarbons: (C x H x ) compounds made up of only carbon and hydrogen. 2 types of Combustion 1.Complete Combustion 2.Incomplete Combustion

Complete Combustion Occurs under conditions in which excess (more than enough) oxygen is present. General Reaction: C x H x + O 2  CO 2 + H 2 O + energy Example: The combustion of ethyne 2C 2 H 5 (g) + 5O 2 (g)  4CO 2 (g) + 2H 2 O(g) + energy

Incomplete Combustion “Fuel rich” combustion, in which the supply of oxygen is limited Occurs when burning a hydrocarbon in an enclosed space Flames are sooty, yellow, and cooler

Incomplete Combustion Produces the same products as complete combustion, but also releases carbon monoxide and/or soot - a solid black ash represented as C(s). Two equations for incomplete combustion: C x H x + O 2 (g)  C(s) + CO(g) + CO 2 (g) + H 2 O(g) C x H x + O 2 (g)  CO(g) + H 2 O(g)

Incomplete vs Complete Combustion Example: The combustion of Hexane. – The 2 equations for incomplete combustion: C 7 H 16 (l) + 7O 2 (g)  3C(s) + 2CO(g) + 2CO 2 (g) + 8H 2 O(g) 2C 7 H 16 (l) + 11O 2 (g)  14CO(g) + 8H 2 O(g) – Complete combustion: C 7 H 16 (l) + 11O 2 (g)  7CO 2 (g) + 8H 2 O(g) More O2 per heptane for complete combustion

Concerns related to Incomplete Combustion Health concerns – Soot particles are an inhalation hazard – can lead to respiratory problems, including asthma – Carbon monoxide an inhalation hazard – can be fatal Releases only a portion of the energy – in a car engine fuel is burned more completely during highway driving.

Homework Page 197 # 1, 2a, 3-7