Topic 8 - Fuels And Earth Science Flashcards
What is a hydrocarbon?
Compounds that only contains hydrogen and carbon atoms
What substance is the main source of hydrocarbons?
Crude oil
What is crude oil?
A complex mixture of lots of different hydrocarbons. The compounds found in crude oil have their atoms arranged in either chains or rings and are mostly alkanes
What is the general formula for an alkane?
Cn H2n +2
What can crude oil be separated into?
Fractions
Is crude oil renewable or non-remewable?
Non-renewable
How can the different fractions of crude oil be separated?
Fractional distillation
Oil is heated until most has turned into a gas. The gases enter a fractionating column, and the liquid part, bitumen, is drained off at the bottom
What is the temperature gradient of a fractionating column?
Hotter at the bottom, and gets cooler as you move up the column
What are the different fractions of crude oil?
Gases Petrol Kerosene Diesel oil Fuel oil Bitumen
What is a use of gases?
Used in domestic heating and cooking
What is a use of petrol?
Used as a fuel in cars
What is a use of kerosene?
Used as a fuel in aircrafts
What is a use of diesel oil?
Used as a fuel in some cars and larger vehicles, such as trains
What is a use of fuel oil?
Used as a fuel for large ships and also in some power stations
What is a use of bitumen?
Used to surface roads and roofs
What are properties of longer hydrocarbons at the bottom of the fractionating column?
They have higher boiling points
They turn back into liquids and drain out of the column early on
Tend to be less flammable, so ignite less easily
Have a higher viscosity (more thick)
What are properties of shorter hydrocarbons at the bottom of the fractionating column?
They have lower boiling points
They turn to liquid and drain out much later on, near the top where it’s cooler
Tend to be more flammable, so ignite more easily
Have a lower viscosity (more runny)
What is a homologous series?
A family of molecules which have the same general formula and share similar chemical properties
What is the molecular formula for methane?
CH4
What is the molecular formula for ethane?
C2H6
What are two different homologous series of hydrocarbons?
Alkanes and alkenes
How can physical properties of compounds change in a. homologous series?
They can very between the different molecules
For example, the bigger a molecule is, the higher the boiling point will be
What are physical properties of a hydrocarbon determined by?
Intermolecular forces that hold the chains together
What is viscosity?
Measures how easily a substance flows (how thick it is)
In terms of forces, what does it mean if a hydrocarbon has a high viscosity (thick)?
There are stronger forces between the hydrocarbon molecules
Why do hydrocarbons make good fuels?
Because the combustion reactions that happen when you burn them in oxygen give out lots of energy - the reactions are highly exothermic
What are the products of the complete combustion of hydrocarbons?
Carbon dioxide and water
What is the difference between complete and incomplete combustion?
Complete combustion occurs when there is plentiful oxygen, whereas incomplete combustion happens when there is a limited supply of oxygen, so there is not enough to form both carbon dioxide and water
What are the common products of incomplete combustion?
Carbon monoxide and carbon (in the form of soot)
There is not enough oxygen to produce water and carbon dioxide, so carbon monoxide, CO, is produced instead
Why is carbon monoxide dangerous?
Carbon monoxide combines with haemoglobin on red blood cells which prevents oxygen from attaching to the red blood cells. As a result, oxygen cannot be carried around the body
A lack of oxygen due to carbon monoxide poisoning can lead to fainting, a coma or even death
Why is carbon soot, produced in incomplete combustion, dangerous?
The tiny particles of carbon can be released into the atmosphere, and when they fall, they deposit themselves as a black dust called soot
Soot makes buildings look dirty, but they are dangerous because they reduce the air quality and can cause or worsen respiratory problems
What causes acid rain?
When fossil fuels are burnt, mostly CO2 is released. However, some of the products are also other harmful substances such as sulfur dioxide and various nitrogen oxides
What happens during acid rain?
The sulfur dioxide mixes with the clouds, and it forms a dilute sulfuric acid. This then falls as acid rain
Why is acid rain dangerous, especially for animals?
Acid rain causes lakes to become acidic and many plants and animals die as a result
Acid rain also kills trees, damages limestone buildings and stone statues. It can also make metal corrode
Why are nitrogen oxides dangerous?
They can contribute to acid rain and, at ground level, can cause photochemical smog
Photochemical smog is a type of air pollution that can cause breathing difficulties, headaches and tiredness
Why is hydrogen a better fuel to use rather than crude oil?
It is renewable and very clean
The only waste product is water, which isn’t necessarily waste as it is used widely
How does a hydrogen fuel cell work?
The hydrogen combines with oxygen to produce energy
It is often used as a fuel in fuel cells
What are disadvantages of using a hydrogen fuel?
You need a special engine, which is very expensive
Hydrogen gas needs to be manufactured which is also very expensive and often uses energy from another source - and this energy comes from burning fossil fuels, so it almost defeats the purpose of it being a “clean” fuel
Hydrogen is also hard to store and is not widely available
What is cracking?
The process of splitting up long-chain hydrocarbons into shorter hydrocarbons
It turns long, saturated alkane molecules into smaller, unsaturated alkene and alkane molecules
What is thermal decomposition?
When one substance breaks down, it forms at least two new ones when you heat it. This means that you need to break strong covalent bonds which require a lot of energy. A catalyst can often be used to speed up this process
Why is cracking used?
Because there is a higher demand for shorter-chain hydrocarbons than there is for longer-chain hydrocarbons
What conditions does cracking involve?
Heat (400-700 C) Moderate pressure (70 atm) A catalyst (aluminium oxide)
What was the Earth’s atmosphere like in the first billion years?
There were lots of volcanoes, which produced mass amounts of carbon dioxide. There was some steam, methane and ammonia, but the majority was carbon dioxide gas
When things settled down, the early atmosphere was mainly carbon dioxide and water vapour
The water vapour later condensed to form the oceans
After the formation of oceans, what changes happened?
A lot of the carbon dioxide in the atmosphere dissolved into the oceans
Nitrogen was added to the atmosphere through ammonia reacting with oxygen and denitrifying bacteria
Green plants evolved which turned the remaining carbon dioxide into oxygen
Much CO2 got locked up in fossil fuels and sedimentary rocks
What is the atmosphere of the Earth like today?
The build-up of oxygen killed of early organisms that couldn’t tolerate it
Oxygen allowed the development and evolution of more complex life forms, for example animals
The oxygen created the ozone layer (CO3), which blocked harmful rays from the Sun and enabled even more complex organisms to evolve, such as humans
There is virtually no CO2 left in the atmosphere now
What is the test for oxygen?
A glowing split will relight when oxygen is present
How does human activity affect the composition of the air?
The population is increasing, so therefore as a species we are collectively producing more carbon dioxide into the atmosphere
Deforestation means that there are less trees to convert carbon dioxide into oxygen, which is causing the temperature of the Earth to rise, in conjunction with the burning of fossil fuels and cattle rearing
How does the greenhouse effect keep the Earth warm?
The Sun gives out electromagnetic radiation
Some wavelengths pass through the Earth’s atmosphere, but some are reflected back into space
The short wavelengths are absorbed by the Earth, which warms the planet
What are the three greenhouse gases?
Carbon dioxide, water vapour and methane
What happens if levels of greenhouse gases are too high?
It causes an enhanced greenhouse effect - more heat radiation from the Earth is absorbed and less is re-emitted back into space, which is causing the atmosphere to heat up
What does increasing greenhouse gases cause?
Climate change
How is methane contributing to the greenhouse effect?
Methane is produced in the digestive process of certain livestock, such as cows. In conjunction with the growing population causing more cows to be reared, more methane will be released into the atmosphere
What is global warming?
It is a type of climate change and causes other types of climate change, for example changing rainfall patterns
It could cause severe flooding due to the polar ice caps melting. If it happens, it will affect the entire world population
Why is historical data less accurate for looking at climate change than current records?
They are much less precise than current measurements made using instrumental sampling. They’re also much less representative of global levels
Less data was also taken over fewer locations
How can you estimate historical data to get an idea of what the levels of atmospheric carbon dioxide were like?
You can analyse fossils, tree rings or gas bubbles trapped in ice sheets
How can we cut down on fossil fuels?
For example, walking or cycling instead of driving a car if there is only a short distance to travel
How will reducing the amounts of fossil fuels burnt reduce the levels of carbon dioxide in the atmosphere?
Less carbon dioxide will be released because they would not be burnt as frequently. Therefore, the the Earth’s atmosphere would not get as warm, which would prevent climate change and global warming
