SAC 1 PREP CHEM Flashcards
Between peat, brown coal and black coal, which is the better fuel? Why?
black coal is a better fuel as it is more harder, have more carbon, less ash and less mosture which results in a higher energy content. It is also because black coal contains the least water and the highest percenatge of carbon.
To extract fuels from crude oil, fractional distillation needs to occur. Explain this process.
Since crude oil is a mixture of hydrocarbons the hydrocarbons are seperated into a range of factions(similar bp and molecular mass) through the process of fractional distillation.
What is the difference between coal seam gas and shale gas?
natural gas
- coal seam gas is the natural gas absorbed to the surface of coal in coal deposits. (between layer)
- shale gas is trapped inside the shale rock.
How to extract natural gas from coal or shale deposits?
Fracking is used to extract the two by drilling the well into a deposit where the fracking fluid is pumped down to fracture the rock and create fissures to the gas can flow through.
Which released more electrical energy per mole of fuel burnt coal or natural gas (eg methane) or biogas. Why? Rank these fuels in order of less to most electrical enerey produced.
= coal > natural gas > biogas
What are some advantages of using bioethanol over biogas?
Bioethanol burns smoothly and has a low bp, high vaporization and energy content. While biogas has significantly lower energy released per gram.
What does it mean to be carbon neutral?
no net release of CO2 into the atmosphere.
What is the difference between petrodiesel and biodiesel? Compare the performance of petrodiesel and biodiesel using the different properties
- petrodiesel is a long non-polar hydrocarbon with no functional groups. [weak dispersion forces, stored longer].
- lower cloud point
- biodiesel contains a polar ester linkage. [dipole-dipole bonds, high mp, hygroscopic (absorb moisture from air)].
- hydrocaron chain is often longer with two electronegative oxygen atoms -> create dipoles.
- more energy is needed to break the bond leading to higher bp for mixture.
Compare the performance of petrodiesel and biodiesel using the different properties
- Viscosity of biodisel is higher than petrodiesel so it does not flow as easily.
- Petrodiesel has a lower cloud point but withstand colder climates without crystallising and has 10% more energy
- biodiesel is more hygroscopic due to polar bonding (the ability to absorb moisture from the air) -> higher affinity for water.
What is cloud point?
measure of performance at low temp
What is the definition of heat of combustion? What conditions (temperature and pressure) is this measured at? What is the unit?
- heat combustion is the enthalpy change that happens when a fuel burns completely in oxygen.
- the conditions it is measured in is at 298K and 100kPa.
- the unit: kJ/mol
What is a biogas?
(methane) - released in the breakdown of organic waste by anaerobic bacteria.
- energy released per gram of biogas is less than natural gas bc methane content in biogas is lower.
What is bioethanol?
- Uses hydrolysis (starch->glucose) and fermentation.
- Used in fermentation by yeasts which convert it to CO2 and ethanol.
- Not carbon neutral because CO2 is produced in the growing, transport and refining of the fuel.
What is biodiesel?
produced through transesterification when triglycerides or lipids react with an alcohol.
- oils from crops like canola oil, soybean oil, animal fats
Why is biofuels considered renewable?
easily replenished by natural processes as fast or more rapidly than consumed.
