Post-Lab 2

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Dec 6, 2023

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Report your value for the heat of combustion of your biodiesel in kJ/g. Make sure that you include your sample calculations. 1. Compare your answer in Q1 to the heat of combustion for a petroleum diesel and E100, another alternate fuel. Include a reference for where you looked-up the values for the petroleum diesel and E100. Which produces the most energy per gram? Note that our method of heat determination was not very efficient as heat is lost to the surroundings so your value maybe quite low. A quick note on the signs of heats of combustion: As the chemical system is losing energy in the process, the enthalpy of combustion (DHcomb) is always negative. However, in publications and sources for the general public, the negative sign is sometimes dropped (I guess people can’t handle a negative sign!). Be aware of this when searching for values. 2. Heat of combustion for my sample: -5.86 kJ/g Heat of combustion for petroleum diesel: -(46~51) kJ/g Heat of combustion for E100: -(23.4~26.8) kJ/g From the above values, we can conclude that petroleum diesel produces the most energy per gram. Reference: Energy content of biofuel. https://en.wikipedia.org/wiki/Energy_content_of_biofuel (accessed Sep 14, 2023). Though combustion of biodiesel produces CO2, a greenhouse gas, it is labeled as ‘carbon- neutral,’ meaning that it does not increase the net amount of CO2 in the atmosphere. Why? 3. It is noticeable that the biodiesel we used comes from vegetable oil. In this case, the CO2 absorbed by the plants and the CO2 released when the biodiesel is burned are generally equal, meaning that no extra carbon is released to the atmosphere during the process. Is biodiesel a “better” fuel than diesel from crude oil? Explain and support your answer. Note that there is not a ‘right’ answer here, your answer will be based on opinion, but it must be supported with data including the data you obtained in this experiment. 4. From the effectiveness point of view, crude oil is definitely a better choice since it has a heat of combustion of -(42~47)kJ/g, which is higher than that of the biodiesel we made. However, if we consider things in a ecological way, biodiesel will surpass crude oil since it is carbon neutral and won't cause extra pressure to our atmosphere. Post-Lab Thursday, September 14, 2023 21:47

What is the theoretical yield of biodiesel (in g) that you can obtain from your canola oil? Use this reference to determine the canola oil MW ( https://biodieseleducation.org/Production/MolecularweightCalculator.html ). Remember that you balanced this as a part of your pre-lab. Also, remember that you must always check for limiting reagents when doing a calculation like this. 5. Was your product more or less viscous than the starting canola oil? Provide a scientific explanation for this result. 6. Our product is less viscid than the starting canola oil. The starting canola oil is a large molecule due to the triglyceride structure. The product, on contrary, is relatively small since it's monoester. We suppose that since higher intermolecular forces would lead to higher viscosity, the decrease of dispersion forces among the molecules when converting canola oil to the biodiesel resulting in a less viscous product.

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