A-level Chemistry: 3.3.2 Alkanes Part 2
These flashcards explain the sources and effects of vehicle emissions, including unburnt hydrocarbons, nitrogen oxides, and smog formation, and describe how catalytic converters help reduce these pollutants.
Where do unburnt hydrocarbons come from?
Engines (they don't burn all fuel molecules = come out as unburnt hydrocarbons)
Key Terms
Where do unburnt hydrocarbons come from?
Engines (they don't burn all fuel molecules = come out as unburnt hydrocarbons)
How are oxides of nitrogen (NOx) produced?
Produced when high pressure and temperature in car engine causes nitrogen and oxygen atoms in air to react together
Describe how smog (O3) is created?
Hydrocarbons and nitrogen oxides react in presence of sunlight to form ground-level ozone (O3) = major component in smog
Why is ground-level ozones bad? (3x)
Irritates people's eyes and increases respiratory problems + lung damage
How can we remove unburnt hydrocarbons and NOx from exhausts?
By catalytic converters
What is a catalytic converter?
Honeycomb made of ceramic material coated with platinum and rhodium metals
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| Term | Definition |
|---|---|
Where do unburnt hydrocarbons come from? | Engines (they don't burn all fuel molecules = come out as unburnt hydrocarbons) |
How are oxides of nitrogen (NOx) produced? | Produced when high pressure and temperature in car engine causes nitrogen and oxygen atoms in air to react together |
Describe how smog (O3) is created? | Hydrocarbons and nitrogen oxides react in presence of sunlight to form ground-level ozone (O3) = major component in smog |
Why is ground-level ozones bad? (3x) | Irritates people's eyes and increases respiratory problems + lung damage |
How can we remove unburnt hydrocarbons and NOx from exhausts? | By catalytic converters |
What is a catalytic converter? | Honeycomb made of ceramic material coated with platinum and rhodium metals |
Describe how acid rain occurs |
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Name 3 things acid rains destroys |
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What are flue gases? | Gases given out by power stations |
Describe flue gas desulfurisation (how flue gases can be removed from power stations before it gets into atmosphere) |
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What is calcium sulfate (AKA gypsum) used for? | Used to make builders' plaster and plasterboard |
Give the symbol equation for forming NO | N2 (g) + O2 (g) → 2NO(g) |
Give the symbol equation for forming sulfuric acid | SO2(g) + 1/2 O2(g) + H2O(l) → H2SO4(l) |
Give 2 word equations of a catalytic converter converting polluting gases into less harmful products | Carbon Monoxide + Nitrogen Oxide → Nitrogen + Carbon Dioxide Hydrocarbons + Nitrogen Oxide → Nitrogen + Carbon Dioxide + Water |
What are free radicals? | Particles with unpaired electrons |
When do free radicals form? | When a covalent bond spilts equally, giving one electron to each atom |
Why are free radicals very reactive? | ∵ electrons are unpaired |
Example: Reacting Chlorine with Methane What happens after the termination reactions? | Depends on whether there's more chlorine or methane around:
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What are chlorofluorocarbons (CFCs)? | Halogenoalkane molecules where all of hydrogen atoms have been replaced by chlorine and fluorine atoms |
What does Ozone (O3) in upper atmosphere do? | Acts as a chemical sunscreen → absorbs UV radiation from Sun |
How is ozone formed naturally? |
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Explain how CFCs are creating holes in ozone layer (include symbol equations) |
Cl• + O3 → O2 + ClO• ClO• + O3 → 2O2 + Cl•
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Name 3 properties of CFCs | Unreactive, non-flammable & non-toxic |
CFCs are _____ | BANNED |
What can we now use instead of CFCs? | e.g. HFCs (hydrofluorocarbons) & hydrocarbons |
For the conversion of methane to tetrachloromethane: Give the overall equation | CH4 + 4 Cl2 → CCl4 + 4 HCl |
Free Radical Substitution Condition | UV light neeed to break halogen bond |
For the conversion of ethane to 1,1-dibromoethane Give the overall equation | C2H6 + 2Br2 → C2H4Br2 + 2HBr |
For the conversion of ethane to 1,1-dibromoethane Give the pair of propagation steps to form bromoethane from ethane | C2H6 + Br• → C2H5• + HBr C2H5• + Br2 → C2H5Br + Br• |
For the conversion of ethane to 1,1-dibromoethane: Give the pair of propagation steps to form 1,1-dibromoethane from bromoethane | C2H5Br + Br• → C2H4Br• + HBr C2H4Br• + Br2 → C2H4Br2 + Br• |
For the conversion of ethane to 1,1-dibromoethane: Give the termination step that forms butane | 2C2H5• → C4H10 |
Write the symbol equation for when carbon monoxide reacts with nitrogen oxide | 2CO(g) + 2NO(g) → N2(g) + 2CO2(g) |
Represent how calcium oxide is used to remove sulfur dioxide from flue gases by using an equation | \ceCaO(s)+SO2(g)−>CaSO3(s) |
Represent how calcium carbonate is used to remove sulfur dioxide from flue gases by using an equation | \ceCaCO3(s)+SO2(g)−>CaSO3(s)+CO2(g) |
Deduce an equation to show how nitrogen dioxide reacts with oxygen and water to form nitric acid | 4NO2 + 2H2O + O2 → 4HNO3 |
Explain the main economic reason why alkanes are cracked (1) | To produce substances which are more in demand / products with high value |
Suggest why calcium oxide reacts with sulfur dioxide (1) | It is basic/SO2 is acidic | (neutralises the gas) |
Write an equation to show how gypsum (calcium sulfate) is made | CaSO3(s) + 1/2O2(g) → CaSO4 Calcium sulfite is oxidised to calcium sulfate (gypsum) |