Combustion Reactions �A combustion reaction is the reaction of a substance with oxygen, producing oxides and energy. �For a combustion reaction to occur, there must be three things present: fuel, oxygen, and heat. �There are two types of combustion reactions: Complete combustion and Incomplete combustion.
Complete Combustion �The reactant burns with enough oxygen to produce carbon dioxide gas and water vapour. �The hydrocarbon burns with a blue coloured flame and gives off a lot of heat. Hydrocarbon + Oxygen Carbon Dioxide + Water Cx. Hy + O 2(g) CO 2(g) + H 2 O(g) Example: 2 C 8 H 18(l) + 25 O 2(g) 16 CO 2(g) + 18 H 2 O(g) + energy
Incomplete Combustion �The hydrocarbon is burned but there is not enough oxygen to form only the oxides and water, so other products are formed. The products are usually: ▪ Carbon dioxide gas CO 2(g) These 3 may or ▪ Carbon monoxide gas CO(g) may not form ▪ Carbon (soot) C(s) ▪ Water vapour H 2 O(g) Water will always be formed
�The hydrocarbon burns with a yellow coloured flame and gives off a lot of light, but is less efficient at generating heat. Hydrocarbon + Oxygen Carbon Dioxide + Carbon monoxide + Water + Carbon Cx. Hy + O 2(g) CO 2(g) + CO(g) + H 2 O(g) + C(s) Remember not all products must be formed �Example: 3 C 2 H 2(g) + 5 O 2(g) 2 CO 2(g) + 3 CO(g) + 3 H 2 O(g) + C(s)
Steps to balance a combustion reaction 1. Balance the carbon atoms first. 2. Balance the hydrogen atoms next. 3. Balance the oxygen atoms last. If there is an odd number of oxygen atoms at this point, place the coefficient “ 2” in front of the hydrocarbon and repeat steps 1 and 2
Example 1 �Write a balanced chemical equation for the complete combustion of decane. C 10 H 22(l)
Example 2 �Write the balanced chemical equation for the complete combustion of butane.
Example 3 �Write the balanced chemical equation for the incomplete combustion of hexane, given the following partial chemical equation: C 6 H 14(g) + 5 O 2(g) __CO 2(g) + ____ + __H 2 O(g) + ___