Topic 8 - Fuels And Earth Science Flashcards
What are hydrocarbons?
Compounds that contain hydrogen and carbon atoms only.
What is crude oil?
A complex mixture of hydrocarbons
Contains molecules with rings or chains of carbon atoms
An important source of useful substances like fuels and feedstocks for the petrochemical industry
A finite resource
Where can crude oil be found?
Under the sea and ground
What does it mean when crude oil is described as “finite”?
It will run out.
How can crude oil be separated?
Fractional distillation
How does the process of fractional distillation work to separate crude oil?
Crude oil is vaporised before it enters a fractionating column.
The fractionating column is hotter at the bottom than at the top. The vapours rise up and condense at different fractions depending on their boiling points.
Hydrocarbons with low boiling points will be tapped off the top of the column and hydrocarbons with high boiling points will be tapped off the bottom of the column.
Why is crude oil separated?
Unseparated crude oil isn’t very useful but the separated products (such as petrol) are very useful.
Refinery gas is a fraction of crude oil. What are its common uses?
Heating and cooking.
Which fraction of crude oil is used as fuel in cars?
Petrol (gasoline)
Diesel is also less commonly used.
Kerosene is a fraction of crude oil. What is a common use of kerosene?
Aircraft fuel.
Diesel oil is fraction of crude oil. What is it commonly used for?
Fuel for some cars and trains.
Which fraction of crude oil is used for road surfacing and roofs?
Bitumen
Fuel oil is fraction of crude oil. What is it commonly used for?
Fuel for large ships and in some power stations.
How do hydrocarbons at each faction differ?
Boiling points
Ease of ignition
Viscosity
The number of hydrogen and carbon atoms their molecules have
Where in the fractionating column do hydrocarbons with the highest viscosity condense?
Viscosity is how thick and sticky a substance is.
The hydrocarbons with the highest viscosity (like bitumen) are collected at the bottom of the fractionating column.
What are the properties of hydrocarbons that are tapped from the top of the fractionating column, like petrol and refinery gas?
Low boiling point
Highly volatile
Easily ignited
Shorter carbon chains (small molecules)
What is a homologous series?
Series of compounds which:
have the same general formula
Have similar chemical properties
Differ by CH2 (subscript) in molecular formula form neighbouring molecules.
Slight variation in physical properties.
Products from crude oil mostly belong to which homologous series?
Alkane homologous series
What are the only products when a hydrocarbons fuel undergoes complete combustion?
Water (H20) and carbon dioxide (CO2)
True or false?
Energy is given out when a fuel undergoes complete combustion?
True
The reaction is exothermic.
Write a balanced symbol equation for the complete combustion of ethane
2C2(subscript)H6(subscript) + 7O2(subscript) arrow 4CO2 (subscript) + 6H2 (subscript)O
When does incomplete combustion occur? What is required to ensure complete combustion occurs?
Incomplete combustion occurs when there is an insufficient supply of oxygen.
To ensure complete combustion occurs, the reaction should be carried out with excess oxygen.
What are the products of incomplete combustion?
Carbon particulates - soot (C)
Carbon monoxide (CO)
Water (H20)
Write a balanced symbol equation for the incomplete combustion of methane to form carbon monoxide
2CH4 (subscript) 3O2 (subscript) arrow 2CO + 4H2 (subscript) O
Write a balanced symbol equation for the incomplete combustion of methane to form carbon particulates
CH4 (subscript) + O2 (subscript) arrow C + 2H2O (2 subscript)
What are the problems with carbon monoxide?
Carbon monoxide is a toxic gas
It is colourless and odourless and if breathed in can cause death by preventing the red blood cells from carrying oxygen around the body.
What are the problems with incomplete combustion?
Produces carbon monoxide which is toxic and can be fatal if breathed in.
Produces carbon particulates (soot) which cause global dimming and respiratory problems.
Why is sulfur dioxide sometimes produced when burning hydrocarbon fuels?
Some hydrocarbon fuels contain sulfur impurities. When the fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide.
How is acid rain produced?
Sulfur dioxide (produced when combusting impure hydrocarbon fuels) evaporates into the air. It reacts with water in the clouds to form sulfuric acid. This is acid rain.
What problems can acid rain cause?
Corrodes buildings and statues made of limestone.
Kills/damages the vegetation.
Lower the pH of large bodies of water, killing the wildlife.
How are oxides of nitrogen produced from car engines?
The high temperature and pressure of a car engine causes nitrogen and oxygen from the air to react together.
What problems are associated with oxides of nitrogen?
Pollutants.
Produce acid rain with similar effects as SO2 (subscript)
Cause respiratory problems.
What are the advantages of using hydrogen as a fuel in cars?
It releases more energy per kg compared to most other fuels.
Water is the only product so no pollutants.
Renewable source of hydrogen can be extracted from water.
What are the disadvantages of using hydrogen as a fuel in cars?
It is expensive to produce and a lot of energy is required for the electrolysis of water to acquire the hydrogen.
Difficult and dangerous to store hydrogen because it is very volatile and easily ignites.
Name the non-renewable fossil fuel found in natural gas
Methane
Are petrol, kerosene and diesel renewable fuels?
No, they are non-renewable.
They are finite resources which are not being readily replaced.
What is cracking?
Breaking down large hydrocarbons into smaller more useful ones.
Saturated alkanes are cracked into shorter chain alkanes and short chain unsaturated alkenes.
What do the terms saturated and unsaturated mean?
Saturated - only contains single bonds
Unsaturated - contains some C=C double bonds
What type of reaction is cracking?
Thermal decomposition
Why is cracking necessary?
The demand for shorter chain alkenes and alkanes is much greater than the demand for long chain alkanes.
What produced the gases that formed Earth’s early atmosphere?
Volcanic activity
Describe how Earth’s early atmosphere formed
Initially the Earth’s surface was molten with no atmosphere
Cooling caused land masses to solidify
Volcanoes formed on the land masses and released gases which formed the early atmosphere.
What was the Earth’s early atmosphere thought to contain?
Little or no oxygen
Large amount of carbon dioxide
Water vapour
Small amounts of other gases
