Chemistry EOY thing Flashcards
What is crude oil?
Crude oil is a
mixture
of many different compounds. Most of the compounds are
hydrocarbons
How is crude oil made?
Crude oil is formed from the remains of dead plants and animals, particularly plankton.
These organic remains were covered by mud and sand, and buried in the earth.
Over millions of years, these organic remains were compressed under a lot of heat and pressure.
The heat and pressure chemically changed the organic remains into crude oil.
Examples of fossil fuels?
natural gas, coal, crude oil
Fractional distillation with crude oil?
Crude oil is a mixture of hydrocarbons with different boiling points.
The first step is to heat the crude oil to a very high temperature so that all of the compounds are evaporated from liquid to gas.
The hot gaseous hydrocarbons then rise up the fractionating column (because hot gas rises).
As they rise, they cool down, because the top of the column is cooler than the bottom.
The hydrocarbons will condense when they become cooler than their boiling point, and the liquid hydrocarbons then collect in trays and drain out.
The longer chain hydrocarbons condense at the bottom of the fractionating column because they have high boiling points.
Meanwhile the shorter chain hydrocarbons condense at the top of the column because they have much lower boiling points.
Whatare the features of shorter chain alkenes?
Shorter chain alkanes have lower melting and boiling points, so are more flammable, and more volatile.
What is cracking?
Cracking is the process in which larger chain hydrocarbons are split into smaller, more useful hydrocarbons.
What type of reaction is cracking
thermal decomposition reaction
What is a thermal decomposition reaction?
something which uses heat to break something apart
what is catalytic cracking?
First, some long chain alkanes are heated until they vaporise into a gas
Then they’re passed over a hot, powdered aluminium oxide catalyst
This breaks the long chain alkanes into a shorter chain alkane and an alkene
How is steam cracking different to catalytic cracking?
Steam cracking is different because there is no catalyst involved. Instead the vaporised long chain alkane is mixed with steam at very high temperatures.
Why does cracking always produce one alkane and alkene
When a long chain alkane is cracked, there aren’t enough hydrogen atoms to make two alkanes. Hence, cracking will always produce one alkane and one alkene.
what is the difference and similarity between an alkane and an alkene?
Alkenes are similar to alkanes. Alkenes are also hydrocarbons and also an example of a homologous series.
The difference is that alkenes have a double bond between two carbon atoms, whereas alkanes only have single bonds.
Another way to express the presence of the double bond between two carbon atoms is to say that alkenes are ‘unsaturated’.
What feature does the double bond in alkenes give?
makes alkenes more reactive than alkanes
how can we we distinguish between alkanes and alkenes?
The test to distinguish between alkanes and alkenes is the bromine water test.
Bromine water (just bromine dissolved in water) by itself is an orange colour. But when it’s mixed with alkenes, all of the bromine will react, and so the solution loses its orange colour, and turns colourless.
This doesn’t happen when bromine water is mixed with alkanes, because alkanes are not reactive enough to react with bromine water. So when mixed with an alkane, the solution will stay orange.
what is the bromine water test?
to distinguish between an alkane and an alkene
what is an isotope?
atoms of the same element with the same atomic number but a different number of neutrons
how do you calculate relative atmoic mass with percentage abundance of isotopes?
(percentage of isotope A times mass of isotope A) plus (percentage of isotope B times mass of isotope B) over a hundred
what is a hydrocarbon
a compound containing hydrogen and carbon atoms ONLY
what does it mean when alkanes are saturated/
that there are as many hydrogen atoms as possible in each molecule.
what is the general formula for alkanes?
CnH2n+2
what is a fraction?
mixture of molecules of similar chain length and boiling points, which are collected at the same point
are longer or shorter hydrocarbons more viscous and why?
longer hydrocarbons are more viscous as they have longer chain lengths, so there are more intermolecular forces.
are longer or shorter hydrocarbons more volatile and why?
smaller hydrocarbon chain lengths are more volatile due to few intermolecular forces
what does cracking produce?
short chain alkanes and alkenes
