Topic 8.1-8.17 - Fuels Flashcards
What are hydrocarbons?
Compounds which only contain carbon and hydrogen
Describe crude oil
Crude oil is a complex mixture of hydrocarbons, that contain molecules in which carbon atoms are in chains or rings. They are an important source of useful substances (fuels and feedstock for the petrochemical industry) but a finite resource.
Describe and explain the separation of crude oil
-The different hydrocarbons in crude oil each have different boiling points.
-Crude oil is heated until it vaporises and enters the fractionating column
-The hydrocarbon vapours rise up the column until they condense, doing so at different heights based on their boiling point.
-The shortest chain hydrocarbons exit at the cooler top of the column (e.g. gases) and the longest chain hydrocarbons exit at the hot bottom of the fractionating column (e.g. bitumen).
Name and give the uses of the 3 shortest chain hydrocarbons
-Gases for domestic heating and cooking
-Petrol as fuel for cars
-Kerosene as fuel for aircrafts
Name and give the uses of the 3 longest chain hydrocarbons
-Diesel oil as fuel for some cars and trains
-Fuel oil as fuel for large ships and in some power stations
-Bitumen to surface roads and roofs
Explain how hydrocarbons in different fractions differ from each other
As the carbon chain length increases:
-Melting and boiling points increase
-Viscosity (measure of a fluid’s resistance to flow) increases
-The less flammable it is so it is harder to ignite
Explain a homologous series
A series of compounds which have the same general formula but differ by CH₂ in molecular formulae from neighbouring compounds. They have similar chemical properties but show a gradual variation in physical properties, as is displayed by their boiling points.
Describe the complete combustion of hydrocarbon fuels
A reaction in which carbon dioxide and water are produced and energy is given out.
Explain why the incomplete combustion of hydrocarbons can produce carbon and carbon monoxide
If there’s not enough oxygen, some of the fuel doesn’t burn. Solid particles of soot (carbons) and unburnt fuel are released.
Carbon monoxide is also released when there isn’t enough oxygen to produce CO₂
Explain how carbon monoxide behaves as a toxic gas
Carbon monoxide is colourless and odourless. If treated in, it prevents red blood cells from carrying oxygen around the body, which leads to death
Describe the problems caused by incomplete combustion producing carbon monoxide and soot in appliances that use carbon compounds as fuels
-Carbon monoxide is a very toxic gas that causes health problems that lead to death if untreated and is hard to detect.
-Soot contributes to global dimming
Explain how impurities in some hydrocarbon fuels result in the production of sulfur dioxide
Sulfur dioxide is a pollutant produced from the combustion of fuel which contains sulfur impurities with oxygen.
How is acid rain created?
By sulfur dioxide dissolving in rain water
Explain the problems associated with acid rain
-It damages buildings and statues made with limestone
-Reduce the growth of or kill trees and crops
-Lower the pH of water in lakes, killing fish
Explain how and why when fuels are burned in engines oxides of nitrogen are produced
-High temperatures are reached when fuels are burned in engines. At these temperatures, nitrogen and oxygen from the air can react to produce nitrogen monoxide
-This nitrogen monoxide can combine with oxygen in the air to form nitrogen dioxide
-Both are oxides of nitrogen and both are pollutants
What are the advantages of using hydrogen, rather than petrol, as a fuel in cars?
-Hydrogen only produces water as waste when combusted. No CO² , which contributes to global warming, or other pollutants produced
-Hydrogen releases more energy per kg of fuel than petrol
-Petrol is from crude oil, a finite resource - hydrogen isn’t a finite resource
What are the disadvantages of using hydrogen, rather than petrol, as a fuel in cars?
-Storage can be dangerous as hydrogen needs to be stored in highly pressurised containers
-The manufacture of hydrogen uses large amounts of energy that could release carbon dioxide into the atmosphere
Describe the difference between types of non-renewable fossil fuel
-Petrol, kerosene and diesel oil are non-renewable fossil fuels obtained from crude oil
-Methane is a non-renewable fossil fuel found in natural gas
Explain cracking
Cracking is a thermal decomposition reaction where larger alkanes are broken down into more useful smaller saturated alkanes and unsaturated alkenes
Explain why cracking is necessary
Smaller hydrocarbons are useful as fuels because they re more volatile, have lower boiling points and are more flammable than longer chained hydrocarbons
