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The engines in many modern cars perform well using petrol with an octane number of 95 - Leaving Cert Chemistry - Question 6 - 2007
Question 6
The engines in many modern cars perform well using petrol with an octane number of 95. (a) What do you understand by octane number? (b) The structures of two comp... show full transcript
Worked Solution & Example Answer:The engines in many modern cars perform well using petrol with an octane number of 95 - Leaving Cert Chemistry - Question 6 - 2007
Step 1
What do you understand by octane number?
Answer
The octane number is a measure of the ability of a fuel to resist knocking or auto-ignition. Higher octane numbers indicate a greater resistance to these phenomena, which is crucial for efficient engine performance. A fuel with a high octane number is less likely to prematurely ignite, allowing for smoother operation and better overall performance.
Step 2
Step 3
Step 4
Suggest one conversion that could be carried out in an oil refinery on the compound of zero octane number in order to produce a compound of higher octane number.
Answer
One conversion that could be carried out is reforming or dehydrocyclisation of the low-octane compound, which helps to increase the octane number by creating branched hydrocarbons.
Step 5
Draw the structure of the molecule. Would you expect the octane number of benzene to be high or low? Give a reason for your answer.
Answer
The molecular structure of benzene (C6H6) is a planar, cyclic compound with alternating double bonds:
H
|
H-C
| H
H-C---C-H
| |
H-C C-H
|
H
I would expect the octane number of benzene to be high. This is due to its ring structure and unsaturation, which contribute to its stability and resistance to knocking.
Step 6
What effects would be noticed when driving a car if the octane number of the petrol used were too low?
Answer
If the octane number of the petrol used is too low, the driver might notice knocking, pinging, or misfiring in the engine. This can lead to reduced power and performance, as well as potential engine damage over time due to uncontrolled combustion.