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alkenes produce more soot?

[h="1"]Why alkenes produce a sootier flame than alkanes? But alkenes require less O2 to burn!
e.g.

ethane:2C2H6(g) + 7O2(g) --> 4CO2(g) + 6H2O(l)[/h]ethene:C2H4(g) + 3O2(g) --> 4CO2(g) + 2H2O(l)
Original post by jadelamlam
[h="1"]Why alkenes produce a sootier flame than alkanes? But alkenes require less O2 to burn!
e.g.

ethane:2C2H6(g) + 7O2(g) --> 4CO2(g) + 6H2O(l)[/h]ethene:C2H4(g) + 3O2(g) --> 4CO2(g) + 2H2O(l)


The C=C bond is harder to break (higher bond energy) than a C-C bond and so there is more likelihood of elemental carbon being produced as soot by alkenes. The hydrogen from both compounds always is burned.
Original post by jadelamlam
[h="1"]Why alkenes produce a sootier flame than alkanes? But alkenes require less O2 to burn!
e.g.

ethane:2C2H6(g) + 7O2(g) --> 4CO2(g) + 6H2O(l)[/h]ethene:C2H4(g) + 3O2(g) --> 4CO2(g) + 2H2O(l)


You really should have the same coefficient in front of the alkane and alkene, as it really should either be 3.5:4 or 7:8 comparing the O2 needed for the alkene and alkane.

Otherwise, charco is bang on the money (as always). Alkynes are even worse!

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