SC20 Fuels Flashcards
How were fossil fuels made?
they were formed millions of years ago from the remains of dead plants and animals that were trapped in sediments under conditions of heat, pressure and absence of oxygen.
What are hydrocarbons?
compounds that contain hydrogen and carbon atoms only
What are finite resources?
These resources are not made any more (or are being made extremely slowly), which limits the amounts available to us
What are non-renewable resources?
resources that are being used up faster than they are being formed
What is Fractional distillation?
a process used to separate a mixture of liquids
that have different boiling points
What are Fractions?
mixtures of hydrocarbons with similar boiling points
How is crude oil separated into fractions?
- Oil is heated to about 450°C and pumped into the bottom of a tall tower called a fractionating column or fractionating tower, where it vaporizes.
- The column is very hot at the bottom but much cooler at the top. As the vapors rise, they cool and condense at different levels, according to their boiling temperature.
- Heavy fractions (containing large carbon chain molecules) have a high boiling point and condense near the bottom of the column.
- Lighter fractions (containing small carbon chain molecules) have a lower
boiling point and condense further up the column. - The vapours with the lowest boiling points do not condense at all and
leave at the top as a mixture of gases[
Give me the order of crude oil fractions from highest boiling point to lowest.
Gases
petrol
kerosene
diesel oil
fuel oil
bitumen
Name a use for gases
heating and cooking in homes
Name a use for petrol
fuel for cars
Name a use for kurosene
fuel for aircraft engines
Name a use for diesel oil
fuel for diesel engines
cars trains
Name a use for fuel oil
fuel for large ships
Name a use for bitumen
making roads
Why do fractions have different boiling points?
There are tiny forces of attraction (intermolecular forces) between all molecules.
The longer the molecule, the stronger these forces are. The stronger the forces, the more energy is needed to break them and allow the molecules to break away from the liquid and form a gas. So longer molecules have higher boiling points.
State the trend in the properties of the fractions leaving an oil fractionating column.
As you go up the column:
Number of molecules goes down
Boiling point decreases
Becomes easier to ignite
Flow more easily
What are Alkanes?
Alkanes are a type of hydrocarbon molecules, with C-C single bonds.
State the features that members of a homologous series havein common.
- The molecular formulae of neighbouring compounds differ by CH2
- They have the same general formula
- They show a gradual variation in physical properties e.g. boiling
points - They have similar chemical properties
What does the General formula show?
Represents the formula for a whole homologous series
What does the Molecular formula show?
Shows the actual numbers of atoms of each
element in the molecules of these compounds
What does the Empirical formula show?
Shows the simplest whole number ratio of
elements in the molecules
What does the Structural formula show?
Shows all the atoms using subscript numbers
but not the bonds
What does the Displayed formula show?
Shows all the atoms and all the bonds present
in an organic compound
What are fuels?
Fuels are substances that release heat energy when
burned
Give me 2 properties of a incomplete combustion.
- water is produced
- energy is given out (but less than in complete combustion
i.e. less efficient fuel) - carbon monoxide and carbon are produced
When is a combustion reaction classified as complete?
A reaction of a hydrocarbon with a plentiful supply of
air or oxygen
Give me 2 properties of a complete combustion.
- only carbon dioxide and water are produced
- large amount of energy is given out (i.e. makes the
hydrocarbon a good fuel)
When is a combustion reaction classified as incomplete?
a reaction of a hydrocarbon with a limited supply of air or
oxygen
What are the problems with soot?
- Blocks the pipes carrying away waste gases from an appliance
- Blackens buildings
- Breathing problems if it collects in the lung
What are the problems with carbon monoxide?
- Colourless, odourless, toxic gas that binds irreversibly with haemoglobin preventing oxygen combining less oxygen carried sleepy, unconscious, even death
What causes acid rain?
Oxides of nitrogen (reaction due to high temperatures in
car engines) and sulfur (petrol impurity) dissolving in rainwate
What are the effects (problems) caused by acid rain
Lakes and soil become more acidic
Fish die
Crops cannot grow
Buildings and statues made of marble(carbonates) dissolve
What is Cracking?
involves the breaking of large alkane molecules (obtained from crude oil) into smaller
alkanes and alkenes
