Questions about fuels

[Etou]

I can't find any answers for these questions any where in my text book and online and I can't answer them.
Explain why pollutants other than CO2 and water are produced when LPG combusts.
LPG and petrol are both fossil fuels. Why is LPG significantly cheaper in Australia than petrol?
Which fuels are most likely to contain these molecules:
- C7H16
- C13H28
- C2H6
Biodiesel freezes at a higher temperature than petrodiesel, why?
Biodiesel produced from canola has a lower melting point that biodiesel made from animal tallow, why?
Why is the melting point important to the transport industry?

[2130]

1. One source for pollutants to arise from combustion is that LPG is derived from the Fractional Distillation of Natural Gas and Natural Gas can be found with water, sulphur, carbon dioxide and nitrogen. Particulates can also form and are the solid combustion products that result from the LPG mixture's impurities being released after combustion
 
2. The price of LPG in comparison to Petrol can depend on a variety of factors: availability, sourcing, demand, mechanical changes needed in cars to make it a usable fuel source, etc. If a car were to use LPG it would therefore require some sort of mechanical conversion which can be costly (gaseous injection). In addition, the tank used store LPG would consume more boot space. When we look at the fuel economy, LPG also has a "fuel economy that is 20-25% lower than that of Petrol," meaning more fuel is required to travel a certain distance.
http://www.sustainablebusinesstoolkit.com/lpg-vs-petrol-vehicles/

3.
C7H16 --> Naphtha: Chemical industry
C13H28 --> Kerosene: Jet fuel / Diesel / Petrol
C2H6 --> Refinery gas: LPG, feedstock for chemical industry

Its hard to define the boundaries of a hydrocarbon's chain length to that of its purpose. I've taken these ranges from online and the Heinemann textbook (P.5)

4. I think there is a variety of reasons why Biodiesel is less 'resistant' to freezing in comparison to Petrol. For starters, Biodiesel contains ester groups are polar and are also able to form dipole-dipole interactions. Thus more energy is require to ensure that these bonds are overcome to a degree in which biodiesel flows and is considered a liquid, not a solid. On the other hand, Petrol is non-polar and can only form weak dispersion forces. This means that less energy is required to overcome these bonds to a degree in which its liquid state is maintained. (Hope this wasn't too wordy )

I can't accurately remember, as I rarely encountered this question, but Biodiesel's hygroscopic nature may also play a role. These water molecules which it absorbs may freeze due to low temperatures, decreasing its ability to flow as well and may contribute to biodiesel having higher temperature at which its freezes.

5. Canola oil is unsaturated. We can assume this as: it is a liquid at room temperature and derived from plants which have a higher proportion of unsaturated lipids.
Thus when you form Biodiesel from it, there will be a greater number of carbon-carbon double bonds in comparison to the animal tallow. Animal tallow is saturated as it is a fat (solid at room temp)  and a higher proportion of saturated fatty acids reside in animals. With more carbon-carbon double bonds, a biodiesel molecule from canola oil is less able to pack closely together. As a result, the greater distance between molecules causes its intermolecular forces to be weaker resulting in less energy needed (lower temperature) to break the bonds and cause the mixture to melt. So when we consider tallow, its saturated nature allows the Biodiesel to pack closely together causing stronger intermolecular forces. This requires a greater amount of energy (higher temp) to melt the tallow-biodiesel mixture.

6. Wow, this is an unusual question... But my best guess would be to think about volume. You can transport a greater amount of a substance if it is in a solid state rather than a liquid as it consumes less volume. With a lower melting point, perhaps more money is saved when needing to ensure an appropriate temperature that allows the transported substance to be in a solid state.
--> Realised I interpreted the last question wrong. Thanks Miniturtle for clearing that up

I hope this helps!

[Bri MT]

My thoughts for 6 would be about wanting the fuel to flow (which it will do in a liquid but not solid state) so that it can be readily ignited and be used as an energy source.

[2130]

*Face palm*

I'm so silly, you're right Miniturtle. I looked at the question as if it were the substance being transported when really its regarding the fuels ability to be delivered as an energy source for transport....

[Bri MT]

*Face palm*

I'm so silly, you're right Miniturtle. I looked at the question as if it were the substance being transported when really its regarding the fuels ability to be delivered as an energy source for transport....

That's alright!  I'm glad you had a shot at it anyway

[Quinapalus]

4. I think there is a variety of reasons why Biodiesel is less 'resistant' to freezing in comparison to Petrol. For starters, Biodiesel contains ester groups are polar and are also able to form dipole-dipole interactions. Thus more energy is require to ensure that these bonds are overcome to a degree in which biodiesel flows and is considered a liquid, not a solid. On the other hand, Petrol is non-polar and can only form weak dispersion forces. This means that less energy is required to overcome these bonds to a degree in which its liquid state is maintained. (Hope this wasn't too wordy )

I can't accurately remember, as I rarely encountered this question, but Biodiesel's hygroscopic nature may also play a role. These water molecules which it absorbs may freeze due to low temperatures, decreasing its ability to flow as well and may contribute to biodiesel having higher temperature at which its freezes.

I think hygroscopic properties are also used to determine how effective a fuel can be combusted. If biodiesel has water attached to its surface, it will be much harder to combust than a 'dry' fuel (like burning wet wood/dry wood). So the hygroscopic properties of biodiesel means that in this direct comparison with traditional petrol fuels, the petrol fuels are favoured. Of course, there are other considerations to be made (cost, environment, etc.)