DF10 - The Trouble With Emissions Flashcards
What are the main pollutants from vehicle engines?(6)
- Carbon dioxide
- Carbon monoxide
- Hydrocarbons
- Nitrogen Oxide
- Particulates
- Sulfuric Oxides
How is carbon dioxide formed from vehicle engines?
Complete combustion of hydrocarbons (e.g alkanes, alkenes, alcohols, cycloalkanes)
Why do hydrocarbons make good fuels?
Combustion is a very exothermic reaction
What problem does carbon dioxide cause?
The greenhouse effect
What is the greenhouse effect?(3)
- Earth radiates IR into space
- Greenhouse gases absorb some of this and reflect it back
- The build up of CO2 causes an enhanced greenhouse effect, leading to global warming
What problems does global warming cause?(3)
- Destruction of habitats e.g ice cap meltings, leading to species extinction
- Sea level rising
- Freak, stronger storms
How is carbon monoxide formed from vehicle engines?
Incomplete combustion of hydrocarbons (e.g alkanes, alkenes, alcohols, cycloalkanes) due to a limited air supply
What problem does carbon monoxide cause for humans and why?
- Poisoning and internal suffocation
- CO molecules are chemically and physically similar to oxygen molecules
- They can bind to the same sites on haemoglobin molecules in red blood cells as oxygen molecules
- Carbon monoxide molecules are better at binding to haemoglobin molecules
- So less oxygen can be carried around the body
How are hydrocarbons emitted from vehicle engines?
Engines don’t burn all the fuel molecules, so some come out as unburnt hydrocarbons
How is nitrogen oxide formed from vehicle engines?
High temperature and pressure in a car engine causes nitrogen and oxygen in the air to react together
How does nitrogen oxide contribute to the problem of acid rain?
It reacts with water and oxygen in the atmosphere to form nitric acid
What problems does nitrogen oxide cause?
- Acid rain
- Photochemical smog
What are particulates?
Small carbon particles below 2.5x10^-12 m
Where do particulates come from?
- By the incomplete combustion of hydrocarbons in engines
- Power stations
- Volcanoes
What problems do particulates cause?
- Can settle in people’s lungs and cause problems e.g decreased lung function and airway irritation
- Cardiovascular problems e.g heart attacks and strokes
Where does sulphur dioxide come from?
- The burning of sulphur impurities in fuels
- Volcanoes
How does sulphur dioxide contribute to acid rain?
Sulphur dioxide gas enters the atmosphere and reacts with the moisture in it to form sulphuric acid
SO2+H2O==>H2SO3
What problems does acid rain cause? (4)
- Breathing difficulties
- Corrodes limestone buildings and statues
- Kills forests
- Kills life in lakes
Define a “secondary pollutant”
A pollutant not released directly into the atmosphere
How is photochemical smog formed?
Primary pollutants e.g hydrocarbons and nitrogen oxides react in the presence of sunlight to form secondary pollutants e.g ozone
What problems does photochemical smog cause? (3)
- Haziness and reduced visibility in the air
- Respiratory problems
- Eye irritation
What way (other than catalytic converters) can carbon monoxide emissions be reduced?
Oxygenates can be added to petrol
Why is a catalytic converter described as being “3-way” (and what pollutants does it reduce)?
It reduces 3 pollutants:
- Carbon monoxide
- Hydrocarbons
- Nitrogen monoxide
What do catalytic converters consist of?
Platinum/rhodium on a porous support
Give the word equation for the reduction of carbon monoxide
2CO+O2====> 2CO2
Give the word equation for the reduction of heptane
C7H16 +11O2 ====> 7CO2 + 8H2O
Give the word equation for the reduction of nitrogen monoxide
2NO + CO =====> N2 + 2CO2
How do catalytic converters work?
They reduce harmful pollutants into less harmful ones
Why does reducing nitrogen monoxide not work in diesel engines?
They have a higher concentration of oxygen so any reducing agent would be oxidised
What two types of catalysts are used in catalytic converters?
- Platinum
- Platinum alloyed with rhodium
What temperature would a platinum catalyst need to work?
240 degrees c
What temperature would a platinum alloyed with rhodium catalyst need to work?
150 degrees c
What type of fuel would a platinum rhodium alloy catalyst need to work and why?
Lead free fuel as lead would poison it
What two ways are there to remove nitrogen oxides in diesel engines?
- Reducing it by recycling exhaust gases through the cylinder, lowering temperature and thus the amount of NOx formed
- Using ammonia as a catalyst instead
Give the formula for using ammonia as a catalyst for reducing nitrogen oxides
4NO + 4NH3 + O2 ===> 4N2 + 6H2O
What two ways are there to remove sulfur oxides?
- Using ultra low sulfur fuels
- Using calcium oxide to remove them from power station emissions
How are particulates removed from power station emissions?
Using wet scrubbers
How are particulates removed from car exhausts?
Using diesel particulate filters
What do diesel particulate filters contain?
A variety of materials, the most common being ceramic
What methods can the government take to reduce overall pollution? (2)
- Changing laws to reduce emissions e.g vehicles not allowed to pollute above a certain level
- Taxing pollution more highly e.g raise taxes on fuel
How can the population reduce overall pollution?
By changing their behaviour e.g car shares
What are the largest sources of air pollutants? (3)
- Transport
- Industry
- Power generation
