Topic 7 - Organic Chemistry Flashcards
What is a hydrocarbon?
Any compound that is formed from carbon and hydrogen atoms only.
What are alkanes?
The simplest type of hydrocarbon.
A homologous series.
Saturated compounds - each carbon forms four single covalent bonds.
What is the general formula of alkanes?
CₙH₂ₙ₊₂.
What are the first four alkanes?
Methane, ethane, propane and butane.
What is the formula for methane?
CH₄.
What is the formula for ethane?
C₂H₆.
What is the formula for propane?
C₃H₈.
What is the formula for butane?
C₄H₁₀.
Describe the viscosity of hydrocarbons in relation to their chain lengths.
The shorter the carbon chain, the less viscious it is (more runny).
Describe the volatility of hydrocarbons in relation to their chain lengths.
Shorter carbon chains are more volatile (lower boiling points).
Describe the flammability of hydrocarbons in relation to their chain lengths.
Shorter carbon chains are more flammable (easier to ignite).
What is the word equation for complete combustion?
hydrocarbon + oxygen = carbon dioxide + water (+energy)
What happens during combustion?
Both carbon and hydrogen from the hydrocarbon are oxidised.
Why are hydrocarbons used as fuels?
Due to the amount of energy released when they combust completely.
How is crude oil formed?
From the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in mud. Over millions of years, with high temperatures and pressure, the remains turn to crude oil, which can be drilled up from the rocks where it’s found.
What is crude oil?
A mixture of lots of different hydrocarbons, most of which are alkanes.
How are different compounds in crude oil seperated?
By fractional distillation.
How does fractional distilation work?
- The oil is heated until most of it has turned into gas.
The gas enters a fractionating column. - In the column there’s a temperature gradient (hot at the bottom, cooler at the top).
- The longer hydrocarbons have higher boiling points. They condense back into liquids and drain out of the column early on, when they’re near the bottom.
The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it’s cooler. - You end up with the crude oil mixture seperated out into different fractions.
What types of oils come from crude oil and what are they generally used for?
Diesel oil, kerosene, heavy fuel oil and liquid petroleum gas. Provide the fuel for most modern transport.
What does the petrochemical industry use some hydrocarbons from crude oil for?
As feedstock to make new compounds for things like polymers, solvents, lubricants and detergents.
What are organic compounds?
Compounds containing carbon atoms, products from crude oil are an example of this. :(
Why do you get a large variety of products from crude oil?
Because carbon atoms can bond together to form different groups called homologous series.
What are homologous series?
Groups contain similar compounds with many properties in common. Examples are alkanes, alkenes…
Why do short-chain hydrocarbons make good fuels?
They are flammable and in high demand.
Why aren’t long-chain hydrocarbons that useful?
They form thick, gloopy liquids like tar.
What is cracking?
The process where longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones.
As well as alkanes, what other type of hydrocarbon can be produced by cracking?
Alkenes.
What are alkenes used as?
As a starting material when making lots of other compounds and can be used to make polymers.
What are some of the products of cracking useful as?
Fuels, eg. petrol for cars or paraffin for jet fuel.
What type of reaction is cracking?
A thermal decomposition reaction - breaking molecules down by heating them.
How does catalytic cracking work?
Long-chain hydrocarbons are heated to vaporise them. The vapour is then passed over a hot powdered aluminium oxide catalyst. The long-chain molecules split apart on the surface of the specks of catalyst.
What is steam cracking?
Hydrocarbons are vaporised, mixed with steam and then heated at very high temperatures.
What is a general equation for cracking?
Long-chain hydrocarbon molecule = shorter alkane molecule + alkene.
What are alkenes?
Hydrocarbons which have a double bond between two of the carbon atoms on their chain. They are unsaturated.
Why are alkenes unsaturated?
The C=C double bond means that the alkenes have two fewer hydrogens compared with alkanes containing the same number of carbon atoms.
Why are alkenes far more reactive than alkanes?
The C=C double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms.
What are the first four alkenes?
Ethene, propene, butene and pentene.
What is the general formula for alkenes?
CₙH₂ₙ.
Why do alkenes tend to undergo incomplete combustion?
Alkenes only combust completely in a large amount of oxygen but there isn’t enough oxygen in the air for this
What is the equation for incomplete combustion of alkenes?
alkene + oxygen = carbon + carbon monoxide + carbon dioxide + water (+energy).