Please help me with Fuels topic!

[suskieanna]

Hello, I have my first chemistry SAC next week on fuels and thermochemistry topic. I finished making my summary note and now currently working on checkpoints for my revision. However, there were questions like 'what is the overall efficiency of the process  (petrol being converted into mechanical energy, which is used to move the vehicle)', 'the formulae of molecules present in biodiesel are most likely to be in the range: multiple choice question' etc. Am I expected to know things in this detail? My school didn't particularly cover this topic in this much detail.
Also on the edrolo video, there was one question that shows the chemical formulae of hexane and its combustion and asking what type of fuel is being used in the reaction. Do I also have to know the chemical composition of each fuel?

Now I am really confused and don't even know what sort of things to study! Plz, help!

[BigK]

Hey 
With regards to petrol being converted in to mechanical energy it is about 25%-35% efficient in engines. You do not need to necessarily be able to quote this figure for the exam. However VCAA will expect you to know it is less efficient than a fuel cell (about 85% efficient).
As for the formulae of the molecules in biodiesel you need to think about the reaction itself. It the size of the triglyceride will determine the size of the fatty acid methyl esters --> and this can very greatly.
If hexane is being combusted, hexane is the fuel. Hexane itself is a gas not too dissimilar from methane. If you want to put this in terms of a 'type of fuel' it would most likely be LPG.