7. Organic Chemistry Flashcards
What is crude oil?
Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons
How is crude oil formed?
Crude oil is formed over millions of years from the remains of ancient biomass (plants and animals), mainly plankton, that was buried in mud, under layer upon layer of rocks - in high pressures and temperatures
Where is crude oil found?
Crude oil is found in rocks
Why is crude oil a finite resource
It is being used up much faster than it is being formed
What are hydrocarbons?
Hydrocarbons are compounds that contain hydrogen and carbon atoms only
What are most of the hydrocarbons found in crude oil called?
Alkanes
What are alkanes?
- Alkanes are saturated hydrocarbons, which means they contain as many hydrogen atoms as possible for each carbon / for each molecule
- As a result, they have no double carbon bonds
What is a homologous series?
A series of compounds with similar chemical properties, the same general formula and the same functional group
What is the general formula for homologous series of alkanes?
CnH2n+2
What are the first 4 members of the alkanes?
- Methane
- Ethane
- Propane
- Butane
How can the hydrocarbons in crude oil be separated?
The hydrocarbons in crude oil can be seperated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation
What is the difference between each hydrocarbon?
Each type of hydrocarbon have different number of carbon atoms and different boiling points
Longer chain hydrocarbons have a ________ boiling point
Longer chain hydrocarbons have a higher boiling point
Explain how fractional distillation of crude oil works
- The mixture of crude oil is heated and boils, whilst it is being fed to the the bottom of the fractional distillation column
- The column is kept cool at the top and hot at the bottom, so temperature decreases going up
- The gases of hydrocarbons move up the column and condense when they reach the temperature of their boiling points
- Different fractions have different boiling points, depending on how big the hydrocarbons are
- The fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases
- The fractions containing bigger hydrocarbons are collected at the lower sections of the fractionating column
- The different fractions are collected as liquids at different levels, and the liquid fractions are then removed
- The fractions are collected from the column in a continuous process
Give 2 reasons why crude oil is fractionally distilled?
- To separate them into fractions, with molecules with a similar number of carbon atoms together and similar boiling points
- Crude oil straight from the ground does not have much use
What are the distilled fractions of crude oil used for?
The disctilled fractions of crude oils are used to produce:
- Fuels (such as petrol, diesel oil and kerosene)
- Feedstock for the petrochemical industry (which produces solvents, lubricants,
polymers and detergents)
Give a reason why a huge number of different natural and synthetic carbon compounds can occur
The vast array of natural and synthetic carbon compounds can occur due to the ability of carbon atoms to form families of similar compounds
What properties do the size of hydrocarbon molecules affect?
- boiling point
- viscosity
- flammability
What affects the properties of hydrocarbon molecules?
The size of the hydrocarbon molecules
What is viscosity?
Viscosity is a measure of how easily a substance flows and how thick it is
- High viscosity means the substance is thick and it does not flow easily
- Low viscosity means the substance is runny and it flows easily
What happens as the size of a hydrocarbon’s molecules increases (gets longer)?
- The boiling point increases
- The flammability decreases
- The viscosity increases
Why are short chain hydrocarbon molecules more useful?
They are easily flammable, so they make good fuels
Why properties influence how hydrocarbons are used as fuels?
- boiling point
- viscosity
- flammability
What does the combustion of hydrocarbon fuels release?
The combustion of hydrocarbon fuels releases energy, so it is exothermic
What is complete combustion?
Complete combustion is when the hydrocarbon is burned with excess oxygen so that it is completely oxidised
What are the products of a complete combustion of a hydrocarbon?
Carbon Dioxide + Water
What happens in terms of energy during the combustion of hydrocarbons?
The combustion of hydrocarbon fuels releases energy into the surroundings, mainly by heating
What is cracking?
Cracking is the process of breaking down larger, less useful hydrocarbon molecules into smaller, more useful molecules
Why do industries carry out cracking?
There is a high demand for fuels with small molecules (as they have high flammability), so some of the products of cracking are useful as fuels which can be sold
What are the 2 types of cracking?
- Catalytic cracking
- Steam cracking
Explain how cracking works
- The fractionally distilled crude oil is placed in steel vessels called crackers
- It is then heated to vaporise the hydrocarbons
- In catalyctic cracking, the vapour is then passed over a hot catalyst, inducing cracking
- In steam cracking, the vapourised hydrocarbons are mixed with steam and are heated to an even higher temperature which induces cracking
- The hydrocarbons are cracked as thermal decomposition reactions, and breaks down in a random way which produces a mixture of smaller alkanes and also alkenes
What type of reaction is cracking
Thermal decomposition reaction
What are alkenes?
Alkenes are unsaturated hydrocarbons that contain at least one double bond between their carbon atoms
Why are alkenes more reactive than alkanes?
Alkenes are more reactive than alkanes as they have a double carbon bond, which allows alkenes to react in ways that alkanes cannot, such as with bromine water
Explain how we can test for alkenes
We can test for alkenes by reacting it with bromine water, an orange liquid, which will become decolourised if alkenes are present
What are the 2 uses of alkenes?
Alkenes are used:
- To produce polymers
- As starting materials for the production of many other chemicals
What is the general formula for the homologous series of alkenes?
CnH2n
How many fewer hydrogen atoms to alkenes have compared to alkanes?
2
What is a functional group?
A functional group is an atom or group of atoms that gives a ‘family’ of organic compounds their characteristic reactions
What is a homologous series?
A series of compounds with similar chemical properties, the same general formula and the same functional group
What is the functional group of alkenes?
C=C
Can alkenes undergo complete combustion?
Yes