What are fossil fuels?
Give three examples
- Fuels are substances that release energy when burned in air or oxygen
- Coal, natural gas (methane) and oil
How is crude oil formed?
Remains of sea plants and animals that have fallen to the ocean floor
Over million of years they are buried deeper and chemical changes forms the crude oil and gas
Since they are less dense, they movemove upwards through permeable rock until they hit impermeable rock and can't move further
What is crude oil?
Crude oil is a complex mixture of compounds requiring refining before use
What are hydrocarbons?
Compounds containing only the elements hydrogen and carbon
What is a fraction?
They are mixtures of substances of similar size and similar boiling point
How is crude oil separated by fractional distillation?
- Vapourised crude oil enters at the bottomof the column where it is hottest
- As it is heated, substances with small molecules will boil first into a gas a nd condense at the top
- Substances with larger molecules have higher boiling points, therefore condensing futher down, creating different fractions
Are alkanes saturated or unsaturated?
What does this mean?
Saturated, the molecules contain only single covalent bonds between atoms (no double bonds)
What is the general formula for an alkane?
What are the properties of short chain hydrocarbons?
- Smaller, lighter molecules with weaker intermolecular forces
- Low boiling points
- Very volatile (tendency to turn into a gas)
- Low viscosity (runny)
- Ignites easily and burns cleanly
What are the properties of long chain hydrocarbons?
- Longer, heavier molecules with stronger intermolecular forces
- Higher boiling point
- Low volatility
- High viscosity (thick)
- Harder to ignite, smokier flame
Combustion reactions are oxidation reactions...why?
They involve the addition of oxygen to a substance
energy is released
What are the products of complete combustion?
And incomplete combustion?
Carbon dioxide and water
Carbon monoxide and water
Carbon and water
How is sulphur dioxide produced in combustion?
- All fossil fuels contain sulphur as an impurity
- This reacts with oxygen when we burn the fuel and forms sulphur dioxide
- This is a poisonous and acidic gas
S + O2 = SO2
How is nitrogen oxide produced in combustion?
It is formed inside an engine from the spark from the ignition
The high temperatures causes the oxygen and nitrogen to react together
How are particulates produced in combustion?
- Diesel engines burn hydrocarbons with bigger molecules than petrol engines, which often lead to incomplete combustion
- This produces tiny solid particles containing carbon and unburned hydrocarbons called particulates
How does acid rain affect the environment?
Kills plants and aquatic life
Erodes limestone buildings
How does global dimming affect the environment?
- Dark/cold → lack of light for crops, solar panels and plants
- Health problems → links to cancer and asthma
How does global warming affect the environment?
→ extreme weather
→ melting of icecaps, flooding of low lying land as sea levels rise
Ways to reduce pollution from burning fuels
- Electric cars
- Renewable energy
- Removing sulphur dioxide in powerstations from waste gasesby reacting it with bases (calcium oxide/calcium hydroxide)
- Filters on engines (burn off trapped solid)
What are biofuels?
Biofuels are fuels that are made from plant or animal products and are alternatives to fossil fuels
How is ethanol produced?
Ethanol is produced from the fermentation of plants (converts glucose in plants into ethanol using yeast)
C6H12O6 → 2C2H5OH + 2CO2
Glucose yeast ethanol carbon dioxide
Advantages of Ethanol
- Carbon neutral
C2H5OH + 3O2 → 2CO2
6CO2 + 6H2O → C6H12O6 + 6O2
- Renewable resource
- Less polluting to the environment - less acid rain and other pollutants
Disadvantages of Ethanol
- Large impact on land-use
►Land used to grow sugar cane for fuel instead of food - famine in developing countries
►Large areas of rainforest cleared to grow sugar cane leading to loss of habitats and endangered species
How is biodiesel produced?
Vegetable oils such as rapeseed oil and soybean oil can be processed and turned into fuels
Advantages of Biodiesel
- Less harmful to plants and animals as if spilled, it breaks down 5x quicker than diesel
- Less polluting - when it burns there are less particulates and sulphur dioxide
- As fossil fuels start to run out, it will become cheaper
- Carbon neutral
Disadvantages of Biodiesel
- Uses large areas of land to grow crops leading to less food production and famine in developing countries
- Destruction of habitats e.g. orang-utans are under threat of extinction due to large areas of rainforest being turned into palm plantations to produce palm oil for biodiesel
What is carbon neutral?
This means that the amount of carbon dioxide that is given off when the fuel burns is the same as the amount absorbed through photosynthesis, whilst the plants it is made from, grows
Why are no fuels 100% carbon neutral?
CO2 released when:
- fertilising and harvesting crops
- extracting and processing the biofuel
- transporting the plant material and the biofuel
Explain the two ways hydrogen can be used for energy
- Fuel → electrolysis of water (needs water and electricity)
- Fuel cells → more efficient, needs a constant supply of hydrogen and oxygen, energy transferred to electrical energy
Production of H2: 2H2O → 2H2 + O2
Combustion of H2: 2H2 + O2 → 2H2O
Advantages of Hydrogen
- It is a clean fuel as water is the only product. No pollutants made when hydrogen burns and no extra CO2 is added to the air
- Can be classed as a renewable source of energy (only if renewable energy source supp;lies energy for electrolysis)
Disadvantages of Hydrogen