Chemistry topic 7 Flashcards
(12 cards)
What do hydrocarbons contain?
A hydrocarbon is in any compound formed from only carbon and hydrogen atoms.
What is an alkane?
The simplest type of hydrocarbon you can get, general formula CnH2n+2.
The alkanes or a homologous series, group of organic compounds, which react in a similar way. They are saturated compounds - each carbon atom forms for single covalent bonds.
The first for alkanes are methane, ethane, propane and butane.
What is the pneumonic for remembering the first for alkanes?
Monkeys eat peanut butter.
Methane, Ethane, propane, butane.
(1 carbon atom, then 2, then 3, then 4 etc)
Explain how hydrocarbon properties change is the chain gets longer?
Is the length of the carbon chain changes the properties of the hydrocarbon change too.
The shorter the carbon chain, move Ronnie, a hydrocarbon is (less viscous).
The shorter the carbon chain, the more flammable the hydrocarbon is.
The properties of hydrocarbons affect how they used for fuels (short chain hydrocarbons with lower boiling points are used as bottle gases - under pressure as liquids in bottles)
What is complete combustion?
Complete combustion of any hydrocarbon in oxygen releases, lots of energy, only waste products of carbon dioxide and water vapour.
During combustion, both carbon and hydrogen from the hydrocarbon are oxidised.
Hydrocarbons are used as fuel is due to the amount of energy released when combusted.
Giving a balance symbol equation for the complete combustion is simple, just write the leftover amounts (reactants equal products)
What is the equation for combustion?
Hydrocarbon + oxygen (goes to) carbon dioxide + water.
How is crude oil made?
Crude oil is a fossil fuel formed of remains of plants and animals mainly plankton. The high temperature and pressure, has turned them to crude oil, which can be drilled up from rocks where it’s found.
Fossil fuels like coal, oil, gas are called nonrenewable fuels as they take so long to make that being used app much faster than being formed. (Finite resources.)
What is fractional distillation?
Crude oil is a mix of different hydrocarbons most are alkanes, the different compounds are separated by this process.
1) oil is heated, gas enters fractionating column
2) there is a temp gradient in the column (hot at the bottom, gets gradually cooler near top)
3) the longer hydrocarbons have high boiling points. They condense into liquids and drain out of the column earlier on when they near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain much later on at the top where it’s cooler.
4) this eventually forms different fractions, each contains a mixture of hydrocarbons, which all contain a similar number of carbon atoms so have similar boiling points.
What is crude oil’s importance in modern day life?
1) Provides fuel for transport
2) Needed in the petrochemical industry, hydrocarbons from crude oil, are used as feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents.
All the products are examples of organic compounds, the reason they’re such a large variety of them is because carbon atoms combine together to form different groups called homologous series. These groups contain similar compounds with many properties in common. Alkanes and alkenes. Are examples of this series.
What is cracking?
1) short chain hydrocarbons are flammable, make good fuels. Long chain, hydrocarbons form thick liquids, like tar. (Not useful…)
2) longer alkane molecules produced from fractional distillation, I turned into smaller, more useful ones by cracking.
3) some of the products of this process are useful as fuels.
4) cracking, produces alkanes and alkanes. alkenes are more reactive than alkanes, used as a starting material when making other compounds making polymers.
How can you test for alkenes?
Bromine water;
When orange bromine water is added to an alkane, no reaction will happen and it’ll stay bright orange.
If it’s added to an alkene, the bromine reacts with the alkene to make a colourless compound sodium bromine water is decolorized.
what are the different methods of cracking?
Cracking is a thermal, decomposition reaction - breaking molecules down by heat.
The first step is to heat, long chain hydrocarbons to vaporise them.
Then the vapour is passed over a hot, powdered, aluminium oxide catalyst.
The long chain molecule split apart on the surface of the specs of catalyst.
This is catalalytic cracking.
You can also crack hydrocarbons if you vapourise them, mix them with steam, then heat them to a high temp. This is known as steam cracking.
