Fuels and Earth Science (2) Flashcards
What is
crude oil?
a complex mixture of many different hydrocarbons
that is also a finite resource
What are
hydrocarbons?
compounds that contain only hydrogen and carbon
How is
crude oil formed?
it is formed at high temperatures and pressures from the remains of animals and plants that died millions of years ago
What are
fractions?
simpler, more useful mixtures than crude oil
these contain groups of hydrocarbons of similar lengths
What occurs during the
fractional distillation of crude oil?
(intro + 6 steps)
The crude oil is split into separate fractions.
1. The crude oil is heated so that most of it evaporates.
2. It is then pumped into the bottom of a piece of equipment known as a fractionating column. (This fractionating column has a temperature gradient running through it - hottest at the bottom and coldest at the top.)
3. The liquid part (bitumen) is drained off.
4. The gas rises up the column and gradually cools.
5. Different compounds in the mixture have different boiling points, so they condense at different temperatures. This means that they condense at different levels in the fractionating column.
6. The various fractions are constantly tapped off from the column at the different levels where they condense.
Hydrocarbons that have a similar number of carbon atoms have similar boiling points, so they condense at similar levels in the column.
What is the fraction
bitumen
used for?
surfacing roads and the roofs of buildings
What is the fraction
fuel oil
used for?
as fuel for large ships and in some power stations
What is the fraction
diesel oil
used for?
as a fuel in some cars and larger vehicles, such as trains
What is the fraction
kerosene
used for?
as fuel in aircraft
What is the fraction
petrol
used for?
as fuel in cars
What is the fraction
gases
used for?
domestic heating appliances and cooking
Define
hydrocarbon.
any molecule that is formed from carbon and hydrogen atoms only
Define
homologous series.
a family of molecules which have the same general formula and share similar chemical properties
What is the relationship between
hydrocarbon boiling point and chain length?
and why?
As chain length increases, so does boilig point.
This is because the intermolecular forces of attraction break a lot more easily in small molecules than they do in bigger molecules.
A large molecule contains many points along its length where it can be attracted to another molecule. So, even if it can overcome these forces 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 in place.
What is the relationship between
hydrocarbon ease of ignition and chain length?
and why?
As chain length increases, ease of ignition decreases.
This is because shorter hydrocarbons have lower boiling points and tend to be gases at room temperature. These gas molecules mix with oxygen in the air to produce a gas mixture that will burts into flames if it comes into contact with a spark.
What is
viscosity?
how easily a substance flows
What is the relationship between
hydrocarbon viscosity and chain length?
and why?
As chain length increases, viscosity decreases.
This is because the stronger the intermolecular forces between hydrocarbon molecules, the harder it is for the liquid to flow.
What is the general equation for
complete combustion of hydrocarbons?
hydrocarbon + oxygen -> carbon dioxide + water
When do
hydrocarbons undergo incomplete combustion?
when they are burned with insufficient oxygen in the air
What other products are produced in
incomplete combustion?
carbon monoxide and sometimes carbon (in the form of soot)
Why is
carbon monoxide a health hazard?
It binds to the haemoglobin in your red blood cells that normally carry oxygen - so less oxygen is able to be transported around your body. A lack of oxygen in the blood supply to the brain can lead to fainting, a coma or even death
What are the negatives of
soot?
- makes buildings look dirty
- reduces air quality
- can cause or worsen respiratory problems
appliances that produce soot are inefficient as well as dangerous
What
harmful substances does the burning of fossil fuels release?
(3)
- carbon dioxide gas
- sulfur dioxide
- various nitrogen oxides
What is the problem with
sulfur dioxide gas?
and where does it come from?
It mixes with water in the clouds and reacts with them to form dilute sulfuric acid. This then falls as acid rain.
this comes from the burning of sulfur impurities
What are the negatives of
acid rain?
(5)
- causes lakes to become acidic (causing many plants and animals to die)
- kills trees
- damages limestone buildings
- ruins stone statues
- can make metals corrode
What are the negatives of
nitrogen oxides?
(2) and where do they come from?
- contribute to acid rain
- cause photochemical smog
At high temperatures reached inside combustion engines, the nitrogen and oxygen in the air can react to form nitrogen oxides.
What are some
advantages of hydrogen fuel cells?
(3)
- the only waste product is water
- no harmful pollutants are produced
- hydrogen is obtained from water which is a renewable resource
What are some
disadvantages of hydrogen fuel cells?
(4)
- a special, expensive engine is required
- hydrogen gas needs to be manufactured - which is expensive and often use non-renewable energy
- hydrogen is a highly flammable gas - so it is hard to store safely
- hydrogen is not widely available - which can make it more expensive to purchase than regular fuels
What is
thermal decomposition?
breaking molecules down into at least two new ones by heating them
What type of reaction is
cracking?
and what does it involve?
a type of thermal decomposition
involves breaking longer alkanes into smaller, more useful hydrocarbons
What are the
conditions for cracking?
- aluminium oxide (alumina) catalyst
- temperatures of 400-700°C
- a pressure of 70 atmospheres
Describe the process of
cracking.
(3 steps)
- The alkane is heated until it is vaporised.
- It is then passed over the catalyst.
- When it comes into contact with the alumina, it breaks, producing a mixture of short-chain alkanes and alkenes.
What was
Earth like for the first billion years?
(4 key points)
- activity?
- early atmosphere?
- there was instense volcanic activity
- the volcanoes gave out a lot of gas
- the early atmosphere contained carbond dioxide with little or no oxygen
- volcanic activity released nitrogen, water vapour, methane and ammonia which would have built up over time
How was
most of the carbon dioxide in the early atmosphere removed?
- absorption by the oceans
- absorption by plants and algae
What is the word equation for
photosynthesis?
and what is the symbol equation?
carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
Describe a
test for oxygen gas.
- Collect the gas in a test tube.
- Put a glowing splint into the test tube.
- If oxygen gas is present, the splint will relight.
What are some examples of
greenhouse gases?
(3)
- carbon dioxide
- methane
- water vapour
Describe the
greenhouse effect.
(4 steps)
- The sun emits short wavelength EM radiation which passes through the Earth’s atmosphere.
- The Earth’s surface absorbs this and re-emits it as long wavelength IR radiation.
- This radiation is absorbed by greenhouse gases in the atmosphere and re-radiated out in all directions - including back towards Earth.
- This warms the surface of the Earth.
What is the
current composition of the Earth’s atmosphere?
78% nitrogen
21% oxygen
some carbon dioxide, noble gases and water vapour
What key areas of human activity have
increased greenhouse gases?
(3)
- increased energy consumption
- deforestation
- methane and farming
What are some
negative consequences of climate change?
- polar ice caps and glacier could melt
- flooding in coastal areas will rise (as well as coastalerosion)
- changes in rainfall patterns may cause some regions to get too much or too little water
- the frequency and severity of storms may increase
