Topic 8 - Fuels and Earth Science

Question 1

What are hydrocarbons?

Answer 1

A compound with hydrogen and carbon only.

Question 2

What are crude oils?

Answer 2

Crude oils are a complex mixture of hydrocarbons. They contain molecules in which carbon atoms are in chains or rings. They are an important finite source of useful substances - fuels and feedstock.

Question 3

Describe Fractional Distillation.

Answer 3

There’s a temperature gradient (it’s hotter at the bottom and gets colder than you go up). Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top. The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.

Question 4

List the most popular fractions and their uses.(6)

Answer 4

Gases - heating and cooking in houses
Petrol - fuel for cars
Kerosene - fuel for aircraft
Diesel oil - fuel for some cars and trains
Fuel oil - fuel for large ships and some power stations
Bitumen - used to surface roads and roofs.

Question 5

How does the size of the hydrocarbon determine its properties?

Answer 5

• The intermolecular forces of attraction break a lot more easily in small molecules than they do in bigger molecules. That’s because the forces are much stronger between big molecules than they are between small molecules. Even if a big molecule can overcome the forces attracting it to another molecule at a few points along its length, it’s still got lots of other places where the force is still strong enough to hold it place. That’s why big molecules have higher boiling points than small molecules do
• Shorter hydrocarbons are easy to ignite because they have lower boiling points, so tend to be gases at room temperature. These gas molecules mix with oxygen in the air to produce a gas mixture which bursts into flames if it comes into contact with a spark. Longer hydrocarbons are usually liquids at room temperature. They have higher boiling points and are harder to ignite.
• Viscosity measures how easily a substance flows. The stronger the force between hydrocarbon molecules, the harder it is for the liquid to flow. Fractions with longer hydrocarbons have a higher viscosity -they’re thick like treacle. Fractions made up of shortened hydrocarbons have a low viscosity and are much runnier.

Question 6

What is a homologous series?

Answer 6

A homologous series is series of compounds which:

• have the same general formula
• differ by CH2 in the molecular formula of neighbouring compounds
• show a gradual variation in physical properties, such as their boiling points
• have similar chemical properties

Question 7

What does the complete combustion of hydrocarbons cause?

Answer 7

Carbon and hydrogen atoms in the fuel react with oxygen in an exothermic reaction:

carbon dioxide and water are produced
the maximum amount of energy is given out

Question 8

What happens in incomplete combustion of hydrocarbons?

Answer 8

If there is not enough oxygen around for complete combustion , you get incomplete combustion. The products of incomplete combustion contain less oxygen. Water is still produced, but carbon monoxide and carbon (in the form of soot) are also produced. Less energy is released than during complete combustion.

Question 9

How is carbon monoxide a toxic gas?

Answer 9

Carbon monoxide can combine with red blood cells and stop your blood from doing its proper job of carrying oxygen around the body. A lack of oxygen in the blood supply to the brain can lead to fainting, a coma or even death.

Question 10

How is soot produced by incomplete combustion bad?

Answer 10

During incomplete combustion, tiny particles of carbon can be released into the atmosphere. When they fall back to the ground, they deposit themselves as the horrible black dust we call soot. Soot makes the buildings look dirty, reduces air quality and can cause or worsen respiratory problems.

Question 11

How do impurities in some hydrocarbon fuels result in the production of sulfur dioxide?

Answer 11

Many hydrocarbon fuels naturally contain sulfur impurities. When the fuels are burned, the sulfur oxidises to form sulfur dioxide gas. Sulfur dioxide dissolves in water in the clouds to form sulfurous acid: Oxygen in the air reacts with sulfurous acid to form sulfuric acid.

Question 12

What are the problems associated with acid rain?

Answer 12

Acid rain causes lakes to become acidic and many plants and animals dies as a result. Acid rain kills trees, damages limestone buildings and stone statues and can also make metal corrode.

Question 13

How are oxides of nitrogen produced when fuels are burned in engines?

Answer 13

High temperatures are reached when fuels are burned in engines. At these high temperatures, nitrogen and oxygen from the air can react together to produce oxides of nitrogen such nitrogen monoxide. Oxides of nitrogen are atmospheric pollutants. They can react in sunlight with other substances to produce a hazy, harmful smog - Photochemical smog. Nitrogen dioxide is toxic. It can cause bronchitis and other lung diseases. It also dissolves in water in the clouds, forming an acidic solution that contributes to acid rain.

Question 14

What are the advantages of have hydrogen instead of petrol as fuel?

Answer 14

• Clean fuel
• No harmful waste products only water
• Renewable resource

Question 15

What are the disadvantages of using hydrogen as a fuel instead of petrol?

Answer 15

• You need a special, expensive engine
• Manufacture of hydrogen is expensive and uses fossil fuels anyway to make it
• Hydrogen is hard to store and not widely available

Question 16

What type of energy resource is petrol, kerosene and diesel oil?What about methane?

Answer 16

Non-renewable . Methane is also non-renewable but is found in natural gas not crude oils.

Question 17

What is cracking?

Answer 17

Cracking is a reaction in which larger hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules, some of which are unsaturated:

• the original starting hydrocarbons are alkanes
• the products of cracking include alkanes and alkenes, members of a different homologous series

Question 18

Why is cracking necessary?

Answer 18

Cracking is important for two main reasons:

• it helps to match the supply of fractions with the demand for them
• it produces alkenes, which are useful as feedstock for the petrochemical industry

Question 19

What is supply and demand in cracking?

Answer 19

The supply is how much of a fraction an oil refinery produces. The demand is how much of a fraction customers want to buy. Fractional distillation of crude oil often produces more of the larger hydrocarbons than can be sold, and less of the smaller hydrocarbons than customers want.

Smaller hydrocarbons are more useful as fuels than larger hydrocarbons. Since cracking converts larger hydrocarbons into smaller hydrocarbons, the supply of fuels is improved. This helps to match supply with demand.

Question 20

What is the difference between alkanes and alkenes?

Answer 20

Alkanes and alkenes both form homologous series of hydrocarbons, but:

• alkanes are saturated (their carbon atoms are only joined by C-C single bonds)
• alkenes are unsaturated (they contain at least one C=C double bond)

As a result, alkenes are more reactive than alkanes. Alkenes can take part in reactions that alkanes cannot. For example, ethene molecules can react together to form poly(ethene), a polymer.

Question 21

How was the early atmosphere formed?

Answer 21

The Earth’s surface was originally molten for many millions of years. There was almost no atmosphere.
Eventually the Earth’s surface cooled and a thin crust formed, but volcanoes kept erupting, releasing gases from inside the Earth. This ‘degassing’ is mainly carbon dioxide, but also steam, methane and ammonia. When things finally settle down, the early atmosphere is mostly CO, and water vapor. There was very little oxygen

Question 22

What did the early atmosphere contain?

Answer 22

The early atmosphere probably contained:

• little or no oxygen
• a large amount of carbon dioxide
• water vapour
• small amounts of other gases, such as ammonia and methane

Question 23

How were oceans formed?

Answer 23

The water vapour in the atmosphere condensed to form oceans.

Question 24

How did the amount of CO2 in the atmosphere decrease?

Answer 24

The CO2 dissolved into the oceans.

Question 25

How did the amount of nitrogen increase in the atmosphere?

Answer 25

Nitrogen gas (N2) was then put into the atmosphere in two ways -it was formed by ammonia reacting with oxygen, and was released by denitrifying bacteria. N2 isn’t very reactive. So the amount of N2 in the atmosphere increased, because it was being made but not broken down

Question 26

How did the growth of green plants increase oxygen levels and decrease CO2 levels?

Answer 26

Next, green plants evolved over most of the Earth. As they photosynthesised, they removed CO2 and produced O2. Thanks to the plants, the amount of O2 in the air gradually built up and much of the CO2 eventually got locked up in fossil fuels and sedimentary rocks.

Question 27

What is the chemical test for oxygen?

Answer 27

You blow a lit splint and put the glowing splint in a test tube of the gas. If the splint relights, then oxygen is present.

Question 28

What did the formation of the ozone layer do?

Answer 28

This blocked harmful rays from the Sun and enable even more complex organisms to evolve.

Question 29

Describe the greenhouse effect

Answer 29

Infrared radiation from the Sun is only partly absorbed by the Earth. The rest is radiated into the atmosphere. Although some of the infrared radiation escapes, some is absorbed by greenhouse gases. This keeps the energy in the atmosphere, warming it up. This gradual warming of the atmosphere over many years is referred to as global warming.

Question 30

How is human activity causing climate change?

Answer 30

The increase in carbon dioxide from burning fossil fuels and the increase in methane from an increase in cattle farming, means that there is more greenhouse gases in the atmosphere which means that less heat is able to escape and more is coming in so the overall temp of earth is increasing.
The effects of this include:
- glaciers and polar ice melting
- sea levels rising
- rainfall changing, producing floods or droughts
- habitats changing

Question 31

Why is historical data of the global temp and CO2 levels inaccurate?

Answer 31

This is because less data was taken over fewer locations and the methods used to collect the data was less accurate. But there are ways to estimate them: fossils, tree rings or gas bubbles trapped in ice sheets. The problem is though is that it is less precise than the instruments we use today.

Question 32

How can climate change be prevented or slowed down?

Answer 32

• Cut down of emission of greenhouse gases
• Limit the use of fossil fuels
• Using renewable energy resources