SC20/21: Fuels, Earth and Atmospheric Science Flashcards
SC20a Hydrocarbons in crude oil and natural gas
Define/Describe the following;
A) Hydrocarbons
B) Crude Oils
A) Hydrocarbons are compounds that only contain hydrogen and carbon atoms only.
- Formula is ( 2n + 2 where ‘n’ = amount of carbon atoms )
B) Crude oils are;
- Complex mixtures of Hydrocarbons
- Containing molecules in which carbon atoms are in chains or rings.
- Also an important source of usefull substances ( fuels & feedstock for petrochemical industry )
- A finite resource
- Liquid at room temp.
Petrochemical - substances made from crude oils, such as polythene and other polymers
SC20b Fractional distillation of crude oil
Explain the process of fractional distillation for crude oils into more usefull mixtures.
Crude oils is heated strongly to evaporate it, and hot vapours are piped into the bottom of the coloum, where;
- The coloumn is hottest at bottom, coldest at top
- Vapours rise through the column and cools down
- The vapours condense when they reach a part of the coloumn that is cool enough ( below boiling points )
- The liquid falls into a tray and is piped away
- Vapours with lowest boiling points do not condense at all and leave at the top of as a mixture of gases
- Bitumen has the highest boiling point and leaves at the bottom as a hot liquid.
Seperated oils and gases are called oil fractions
SC20b Fractional distillation of crude oil
Recall the names and uses of the main fractions leaving the fraction column
( Lowest Boiling Point ) 1. Gases -> Used for domestic heating and cooking
2. Petrol -> Used as fuels for cars
3. Kerosene -> Used as fuel for aircrafts
4. Diesel oil -> Used as fuel for some cars and trains
5. Fuel oil -> Used as fuel for large ships and power stations
( Highest Boiling Point ) 6. Bitumen -> Used for surfacing roads and roofs.
SC20b Fractional distillation of crude oil
Explain how Hydrocarbons in different fractions are different from eachother.
( Refer to properties )
- Hydrocarbons in the gases fraction have the lowest visocisty ( they flow easily ) and are easiest to ignite ( they are set alight easily ), making them suitable for fuels.
- The higher up the fractioning coloumn a fraction leaves, the lower their boiling point is, and vice versa
- The higher up the fractioning coloumn a fraction leaves, the less carbon atoms the Hydrocarbon tends to have.
- As mentioned before, viscosity and ignitability both increase as you go higher up the fractioning column.
SC20c The alkane homogus series
Describe what is ment by a homologous series.
1. The compounds in crude oils are mostly alkanes. Alkanes are Hydrocarbons that only have single covalent bonds between atoms in their molecules
- The alkanes form a homologous series of compounds
2. Members of a series have the following in common.
- The molecular formulae of neighbouring compounds differ by CH2
- They have the same general formula
- They show a gradual variation in physical properties, like boiling points.
- They have similar chemical properties.
SC20d Complete and incomplete combustion
A) Describe what is ment by a complete combustion
B) Describe what is ment by an incomplete combustion
A1) These are reactions of Hydrocarbons in which;
- Only carbon dioxide and water are produced
- Energy is given out.
A2) Complete combustions happen when their is a plentiful supply of air or oxygen, Methane is the main hydrocarbon found in natural gases.
B) Incomplete combustions occur when their is a limited supply of of air or oxygen, during the incomplete combustion of a hydrocarbon;
- Water is produced
- Energy is given out ( less than that of complete combustion )
- Carbon monoxide, CO, and carbon are produced.
- Some carbon atoms are released as carbon or soot.
SC20d Complete and incomplete combustion
Describe the issues caused by incomplete combustion
- Incomplete combustion can cause problems in appliances that use hydrocarbon fuels, such as boilers or heaters, if they are poorly maintained.
- Carbon monoxide is a toxic gas. It combines with the haemoglobin in red blood cells, preventing oxygen combining.
- This reduces the amount of oxygen carried around in the blood stream, causing affected people to feel sleepy or to become unconscious, can even lead to death.
- Soot can block the pipes carrying away waste gases from an ppliance. It blackens buildings and can cause breathing problems if it collects in the lungs
SC20e Combustible fuels and pollution
Explain the process of how Acid rain is produced.
How it’s produced:
1. Hydrocarbon fuels may contain sulfure compounds. These occur naturally as impurities.
- While most of these impurities are removed at the oil refineries, issues arise if they are not.
2. When Hydrocarbon fuel is burnt, the sulfur reacts with oxygen to form sulfure dioxide.
- S + O2 -> SO2
3. Suflur dioxide dissolves in the water in clouds to form a mixture of acids, including sulfurous acids.
- H20 + SO2 -> H2SO3 ( aq )
4. Sulfurous acid is oxidised by the air to form sulfuric acid.
- 2H2SO3 + O2 -> 2H2SO4
SC20e Combustible fuels and pollution
Describe the problems caused by Acid rain
Problems caused;
- When this mixture of sulfurous acids and sulfuric acid fall as acid rain, problems arise.y
- Crops do not grow well when soil is too acidic
- Excess acidity in rivers and lakes prevent fish eggs hatching, and it can kill fish + insects
- Acid rain increases the rate of weathering for buildings made of limestone or marble, and breaks down their strucures.
- Reaction: Calcium Carbonate + Sulfuric Acid -> Calcium sulfate + water + carbon dioxide.
- Acid rain also increases the rate of corrosion of metals, such as iron in steel, weaking them
- Reaction: iron + sulfuric acid -> iron(II) sulfate + hydrogen
SC20e Combustible fuels and pollution
Explain what happens when fuels are burned in engines of cars.
1. Car engines are ‘internal combustion’ engines - fuel is mixed with the air and ignited inside of the engine.
2. This causes temperatures high enough for the oxygen and nitrogen in the air to react together.
- The reaction produces various oxides of nitrogen, ( NOx ) which are atmosphereic pollutants
3. NOx are a cause of acid rain, NO2 forms dilute nitric acid when it dissolves in the water in clouds.
- NO2 is a toxic red gas that can cause respiratory diseases such as bronchitis.
4. Catalytic converters in cars convert most of the NO2 in exhaust gases into harmless nitrogen.
SC20f Breaking down hydrocarbons
Explain the process of cracking and why it is needed.
What it is: Cracking involves breaking down covalent bonds in larger saturated alkanes into smaller, more usefull ones that are sometimes alkenes.
Process;
- The Hydrocarbon vapours from a crude oil fraction are passed over a catalyst containing aluminion oxide and heated to about 650C
- This speeds up the reaction to break down the larger Hydrocarbon molecules.
Why it is done?
- Demand for many shorter alkanes is higher than the supply, so cracking is used to fill that supply gap.
SC20f Breaking down hydrocarbons
Evaluate the advantage & disadvantages of using;
A) Hydrogen
B) Petrol
In fuel for cars.
A1) Hyrodgen Advantages;
- The combustion of hydrogen produces water vapour but no CO2, making hydrogen fuel benefitial globally due to not producing a greenhouse gas.
- Hydrogen ignites very easily
- Hydrogen releases more energy per J than petrol
- It is renewable aswell.
A2) Hydrogen disadvantages
- Since hydrogen is a gas at room temp, meaning it is not easy to store and needs to be liquidified by cooling first.
B1) Petrol Advantages;
- It ignites very easily
- It releases alot of energy when combusted ( Not as much as Hydrogen )
- It can be stored easily due to it being a liquid at room temp
B2) Petrol Disadvantages;
- It is non-renewable, meaning it is a finite resource
- The combustion of petrol releases greenhouse-gases ( CO2 e.g. ) into the atmosphere, causing global warming and such.
- Releases less energy than Hydrogen when combusted.
Note 1: Petrol, Kerosene and diesel oil are non-renewable fossil fuels released from crude oil.
Note 2: Methane is a non-renewable fossil fuel found in natural gases.
SC21a The early atmosphere
Describe what Earths early atmosphere is thought to of been like, relate this to evidence by scientists.
1. It is believed earth’s early atmosphere was; mainly carbon dioxide, had little or no oxygen, small amounts of water vapour & other gases
2. Volcanoes affect the atmosphere by releasing large amounts of; carbon dioxide, water vapour and other gases ( nitrogen )
- There was alot of volcanic activity on early earth, which probably contributed to our atmosphere
3. The atmospheres of Venus and Mars are like earth ( containing alot of CO2 ) and they also have volcanoes, supporting the idea of volcanoes helping to shape atmosphere.
4. Some scientists think the Earth’s atmosphere was mainly nitrogen. Evidence for this come from Titan, a moon of saturn. Titan’s atmosphere is 98.4% nitrogen, probably also released by volcanous.
- However Titan has an icy interior, unlike Earth. Meaning that it’s less likely Earth was like Titan.
SC21a The early atmosphere
Describe how Earth’s oceans may have formed.
- About 4 billion years ago, the Earth cooled down. This water vapour in the atmosphere to condense to liquid water, which formed the oceans.
SC21a The early atmosphere
Explain the evidence that oxygen was not present in early Earth atmosphere.
- Oxygen is not produced by volcanoes. Further evidence come from iron pyrite, a compound that is broken down by oxygen, meaning it only forms if there’s no oxygen. It is often found in ancient rock.
- Around 2.4 billion years ago, rocks containing bands of iron oxide started to form. This oxidation suggests that oxygen levels began to rise around this time.
- There is fossil evidence this oxygen was produced by microorganisms.
- Some geologists think that it was only after microorganisms had produced enough oxygen to oxidise the iron in the ocean the oxygen levels could rise.
SC21b The changing atmosphere
Explain how the amount of carbon dioxide decreased when oceans formed.
- As the young Earth cooled, water vapour in the atmosphere condensed and formed oceans.
- Many scientists think that carbon dioxide dissolved in the oceans, reducing the amount of CO2 in the atmosphere.
- Sea creatures used the dissolved CO2 to form shells made of calcium carbonate, CaCO3. This then allowed more CO2 to dissolve in the sea.
SC21b The changing atmosphere
Explain how the growth of plants led to an increase in oxygen levels.
- Some organisms use energy from the sun to make food via photosynthesis.
- Photosynthsis uses up carbon dioxide and oxygen is a product of it, meaning oxygen is released.
- Some of the earlist photosynthetic organisms were cyanobacteria, which lived in shallow waters.
- These bacteria grow in large colonies and produce sticky mucus. The mucus traps a layer of sand and other sediments.
- The organisms need to move above the sediment layer in order to reach the light.
- Overtime the sediment layers build up to form rocky shapes, called stromatolites.
SC21c The atmosphere today
Explain what is ment by the greenhouse effect
- Energy from the sun is transferred to the Earth by waves, such as light & infared. Some energy is absorbed by the Earth’s surface, warming it up.
- The warm Earth emits infared waves. Some gases in the air absorb energy transferred by these infared waves.
- Some gases in the air absorb energy transferred by these infared waves. When the gases re-emit the energy, some of it goes back to the earth and warms it. This is called the green house effect.
- Green house gases ( gases in the atmosphere that absorb and release energy ) are; carbon dioxide, methane and water vapour.
SC21c The atmosphere today
Describe the correlation between human activity and climate change
1. Since about 1850, there has been a steady increase in the amount of fossil fuels burned for industry.
- During this time period, CO2 levels have increased
- Since we know combustion produces CO2, this is good evidence that increased fossil fuel use has caused increase in CO2 levels.
2. As CO2 levels have risen, so has the average temperature on the Earth’s surface. There is a strong correlation between CO2 levels and surface temperature.
3. Scientists can show that CO2 absorbs infared, Satellite data also confirms that as CO2 levels have increased, there has been a decrease in infared rays leaving the Earth.
- This supports that idea that CO2 causes temperature rises.
SC21c The atmosphere today
Describe how evidence surrounding climate change can be and has been evaluated.
1. The amount of carbon dioxide today is measured at monitoring stations around the world.
- Evidence for historical carbon dioxide levels comes from measuring concentrations of gas trapped in ice cores.
2. The oldest continous temperature records are for central England and go back to 1659.
- However, these records cannot be used to asses global temperatures as they are only from 1 location.
- Continous temp measurements from around the world exist from 1880.
3. While early measurements were not very accurate, Modern themometer are less prone to error and have a greater resolution.
SC21d Climate change
Describe different human activities that may have contributed to climate change.
1. Increased fossil fuel usage
- Increasing fossil fuel burning is increasing the amount of CO2 released into the atmosphere, which is thought to be causing global warming
- CO2 is not the only green-house gas.
2. Methane emissions
- Methane is much more powerful greenhouse gas than CO2 due to it being able to absorb much more infared radiation than CO2.
- Methane is the main component of natural gas, and is released when natural gases and oils are extracted from the ground & processed.
3. Livestock farming
- This produces alot of Methane
- Cattle have bacteria in their stomachs to help them digest grass.
- Some of the bacteria produce methane.
- Soil bacteria in landfill sites and in rice ‘paddy’ fields also produce alot of methane.
SC21d Climate change
Describe the effect of the climate change on the atmosphere today.
1. Rising global temperatures will cause ice at south pole & glaciers to melt. The extra water will cause sea levels to rise which can lead to flooding in some areas,
- It can also lead to a loss of ‘sea ice’ at the poles
2. Some animals may move away from their natural habitats to find cooler areas. Some animals may go extinct if they cannot survive at warmer temperatures.
3. As weather patterns change, some area will become drier than others and some will be wetter. Scientists predict there will be extreme weather events
- These changes will affect wildlife & the growth of crops that people need.
4. As more CO2 is released, more of the acidic gas will dissolve in sea water, lowering its ph. This can harm sea life.
- Additionally, as temperature rises, it causes coral to push out the photosynthetic algae that live in their tissue.
- These algae provide the ‘colour’ for corals, so coral bleaching may occur.
SC21d Climate change
Describe how the effects of climate change can be mitigated.
1. Using renewable energy sources can reduce green-house gas emissions, but there is a risk it may not be enough to mitigate things we are already seeing.
2. Some have suggested global engineering fixes, to reflect sunlight back into space or to capture CO2 from the air and bury it underground.
- However mass coordination from countries would b needed, it may also disrupt delicate ecosystems
3. Also, helping people adapt to new conditions can help. These include; flood defences, dams and irrigations systems. However, these ideas may destroy important habitats & there is a risk they won’t work.
