SolutionsFuels and Energy
1. Balance the combustion
Write and balance the complete combustion of propane, C3H8, and of octane, C8H18.
- C3H8 + 5 O2 → 3 CO2 + 4 H2O
- 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
2. Octane number
What are the octane numbers of heptane and 2,2,4-trimethylpentane? Why are the chains of petrol branched?
Heptane has an octane number of 0 and 2,2,4-trimethylpentane (isooctane) of 100. Branched alkanes burn more progressively and resist self-ignition (“knocking”) in the engine better; that is why the proportion of branched chains is increased by isomerization and reforming.
3. Biodiesel
Which reaction turns a vegetable oil into biodiesel, and which by-product is formed?
A base-catalysed transesterification with methanol: the triglycerides are turned into the methyl esters of the fatty acids (biodiesel) and glycerol is released.