Topic 8 - Earth Chemistry

Topic 8.1 and Topic 8.2

8.1 

Hydrocarbons are compounds made of only hydrogen and carbon atoms. 

8.2 

Crude oil is a complex mixture of hydrocarbons.

The carbons are arranged in chains or rings.

It is an important resource in the petrochemical industry and fuels/feedstock. 

Crude oil is a finite resource as it takes millions of years to produce. 

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Topic 8.3

Fractional Distillation is used to seperate crude oil into different 'fractions' each containing a different substance. 

The Crude Oil is heated until the majority is turned into gas. The gases then enter the fractionating column which has a temperature gradient (It is hottest at the bottom of the column).

The hydrocarbons with the longest chains have much higher boiling points, and so they turn into liquids much quicker and drain out of the column much quicker.

Shorter chained hydrocarbons condense nearer the top of the fractionating column where it is much cooler.

Each fractions contain a different mixture of hydrocarbons, most of which are alkanes. 

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Topic 8.4

Fraction names and uses -

Gases - Used in domestic heating and cooking

Petrol - Used as a fuel for cars

Kerosene - Used to fuel aircrafts

Diesel Oil - Used as a fuel for certain cars and trains

Fuel Oil - Used as a fuel for ships and power stations

Bitumen - Used to surface roads and roofs

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Topic 8.5a and Topic 8.5b

In each fraction, the chains of hydrocarbons are very similar lengths, meaning they contain similar amount of carbon and hydrogen atoms. 

Furthermore, The larger molecules have much higher boiling points due to the strong intermolecular bonds. Shorter chains have lower boiling points as it doesnt take much to break these intermolecular bonds. 

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Topic 8.5c and 8.5d

Shorter hydrocarbons are easier to ignite than longer chained hydrocarbons as they have lower boiling points and are usually gases at room temperature. 

The gas molecules form a mixture with oxygen making them burst into flames when they come into contact with sparks. 

Longer hydrocarbons are usually liquids at room temperature and have much higher boiling points, making them harder to ignite. 

Viscosity is how easily a substance can flow. The stronger the force between hydrocarbon molecules, the harder it is for the liquid to flow, therefore it has a higher viscosity. 

Fractions with a low viscosity are much runnier. 

Moreover, these fractions are usually members of the homologous alkane series. 

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Topic 8.6

A homologous series, is a family of compounds that all share: 

The same general formula (e.g alkanes is Cn +H2n+2) 

They all differ by CH2 in molecular formulae.

They show a gradual variation between properties (e.g boiling points increase as the hydrocarbon chain increases. 

They all have similar chemical properties. 

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Topic 8.7

Hydrocarbons are great fuels in combustion reactions. They react with oxygen to form carbon dioxide and water.

These reactions give outs lots of energy, making them highly exothermic. 

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Topic 8.8/8.9/8.10

Incomplete combustion reactions occur when a hydrocarbon burns with a limited supply of oxygen. 

The products from an incomplete combustion reaction is carbon monoxide, a deadly gas and carbon as soot. 

Carbon Monoxide reacts with the haemoglobin in red blood cells. This means the red blood cells carry less oxygen around the body. A lack of oxygen to the brain can cause fainting, dizziness and death. 

Soot is small particulates of carbon. Not only does this make buildings look dirty, it reduces the quality of the air which can lead to or worsen respiratory problems. 

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Topic 8.11 /8.12

Sulphur Dioxide is produced from sulphur impurities from fossil fuels. 

This sulphur dioxide mixes with the clouds to form dilute sulphuric acid, which falls as acid rain. 

Acid rain causes lakes to become acidic causes many plants and animals to die as a result. 

This also kills trees and damages buildings made of limestone and make metal corrode. 

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Topic 8.13

Nitrogen Oxides are created from a reaction between Nitrogen and Oxygen in the air caused by the energy from combustion reactions.

Nitrogen Oxides are harmful pollutants as they contribute to acid rain and photochemical smog.

Photochemical smog is a type of air pollution that can cause breathing difficulties, headaches and fatigue. 

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Topic 8.14

Hydrogen can be used as a clean, renewable fuel.

Pros -

Hydrogen is very clean, It combines with oxygen to produce energy with the only waste product being water, Hydrogen is obatined from water (a renewable source) and can even be obtained from the waste product.

Cons -

It needs an expensive engine to power the vehicle, Hydrogen needs to be manufactured which is expensive and mostly uses energy from non-renewable sources which produces pollutants, Hydrogen is hard to store and is not widely available. 

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Topic 8.15 / 8.16 / 8.17

8.15

Petrol, Diesel and Kerosene are all non-renewable fossil fuels from fossil fuels and methane non-renewable fossil fuel from natural gas. 

8.16

Cracking is the splitting up of long saturated alkane molecules into smaller unsaturated alkene molecules. This is a form of thermal decomposition which breaks down into two new ones once it is heated. A lot of energy is needed for this reaction as you need to break strong covalent bonds, so a catalyst is often used. 

8.17 

Cracking is necessary as there is a much higher demand for smaller hydrocarbons such as petrol and diesel for vehicles rather than fuel oil and bitumen. 

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Topic 8.18 / 8.19

8.18

The gases produced in the earlier atmosphere were mostly from volcanic activity, which means that the early atmosphere was mostly carbon dioxide, but other gases such as steam, methane and ammonia were released too.

8.19 

The early atmosphere is thought to have little or no oxygen with massive amounts of carbon dioxide. There was also lots of water vapour with small amounts of ammonia and methane. 

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Topic 8.20 / 8.21/ 8.22

8.20 

The water vapour in the early atmosphere eventually condensed to form our oceans.

8.21 

The carbon dioxide levels dropped as it was absorbed into the newly condensed oceans. 

8.22 

Primitive plants evolved and grew all over the earth, and plants used carbon dioxide to produce food during photosynthesis. Oxygen is a product of photosynthesis, which mean't that the levels of oxygen in the atmosphere grew. 

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Topic 8.23 / 8.24

8.23 

You can test for oxygen by using the glowing splint test. Collect the gas in a test tube, if oxygen is present it will relight a glowing splint. 

8.24 

In the atmosphere the amounts of carbon dioxide, methane and water vapour all absorb radiation, which is then released energy which then keeps the warm. This is known as the greenhouse effect. The radiation produced by the sun passes through the atmosphere, and waves with the shortest wavelengths are absorbed, which warms the planet. An enhanced greenhouse effect is where more radiation is absorbed and less in re-emitted into space, causing the atmosphere to heat up. 

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Topic 8.25

As the human population increases more and more people are respiring which produces more carbon dioxide.

More people means more energy demands, this increased energy consumption means burning more fossil fuels which releases carbon dioxide.

More land is also needed to grow more food, and more room means more deforestation. Trees are the main removers of carbon dioxide in the atmosphere and store massive amounts of carbon dioxide. Chopping down trees not only reduces natural sinks, but also releases huge amounts of carbon dioxide. 

More naturally, carbon dioxide is also produced by volcanic activity. 

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Topic 8.25 continued

Not only does carbon dioxide cause problems, but methane contributes too. Methane is produced by the digestive bacteria in livestock. It may be present in smaller amounts than carbon dioxide but methane can absorb more heat, and therefore releases more heat. 

The scientific consensus on climate change is that extra greenhouse gases are being produced by anthropogenic (human) causes, ultimately raising the average temperature of the Earth to increase. This leads to global warming. 

Global warming is a form of climate change, which the scientific community mostly believe that humans are contributing to. However, some scientists believe that this is just the Earth's natural fluctuations and that there isn't enough data to prove that climate change is happening. 

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Topic 8.25 continued

The data used for current global temperatures and carbon dioxide levels are much more accurate as they're based on measurements from all over the world. 

Histroical data is less accurate as it was taken over fewer locations and the methods that collected data were much less accurate. 

You can estimate data by analysing fossils, tree rings and gas bubbles trapped in ice sheets. However, these methods are much less precise than current measurements and are less representative of global methods. 

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Topic 8.26

The build up of oxygen in todays atmosphere mean't that organisms that could not withstand it were killed off. 

This lead to the evolution of more complex organisms that use the oxygen. 

The oxygen produced created an o-zone layer (O3) which blocked harmful sun rays and enabled more complex organisms to evolve.

There is virtually no carbon dioxide left. 

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Topic 8.26b

The effects of climate change include -

Rising sea levels leading to the damage of small islands.

The melting of glaciers which not only destroys habitats, but also contributes to the rising sea levels. 

The more carbon dioxide produced, means more carbon dioxide being absorbed by the oceans, meaning fish are killed and coral habitats are bleached and killed. 

More frequent and extreme weather events, which can be caused by the rising global temperatures. 

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Topic 8.26c

To slow down or prevent climate change, humans need to cut down on the release of fossil fuels into the atmosphere. This can be done by reducing our individual fossil fuels by cycling and walking instead of driving. 

However, the government has a massive effect and is transforming plans to encourage the public to become more energy efficient. The government have also introduced incentives such as eco friendly buses. 

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