Organic chemistry Flashcards
(44 cards)
What is a hydrocarbon?
Any compound that is formed from hydrogen and carbon atoms only
What are alkanes?
The simplest type of hydrocarbon you can get. They are a homologous series (react in a similar way) and are saturated compounds (each carbon atom forms four single covalent bonds)
What are the first four alkanes?
Methane, ethane, propane and butane
What is the general formula for alkanes?
C n H 2 n+2
How do hydrocarbon properties change with the chain length?
Shorter chains are more runny (less viscous), more volatile (have lower boiling points) and are more flammable
Give the word equation of the complete combustion of a hydrocarbon
Hydrocarbon + oxygen –> carbon dioxide + water (+energy)
Why are hydrocarbons used as fuels?
They release a large amount of energy when combusted completely
How can fractional distillation be used to separate hydrocarbon fractions?
Oil heated until turns to gas, gas goes into fractionating column, longer hydrocarbons have high boiling points, condense near bottom (hot at bottom), shorter hydrocarbons have lower boiling points, condense at top (cold at top)
What is crude oil used for in modern life?
Fuel for transport and is used used in petrochemical industry to make new compounds in things like polymers, solvents, lubricants and detergents
What is cracking used for?
As short-chain hydrocarbons are more flammable, they make better fuels, so to achieve this, longer hydrocarbons are split up through cracking
What are alkenes?
A type of hydrocarbon used as a starting material when making lots of other compounds and can be used to make polymers
What type of reaction is cracking?
Thermal decomposition - breaking down molecules by heating them
How do you perform catalytic cracking?
Long-chain hydrocarbons are vaporised, vapour is passed over a hot powdered aluminium oxide catalyst, long-chain molecules split apart on the surface of the specks of catalyst
How do you perform steam cracking?
Long-chain hydrocarbons are vaporised, mixed with steam and then heated to a high temperature
What is the structure of an alkene?
They have a double bond between two of the carbon atoms in their chain, meaning that they have two fewer hydrogens compared to the alkane with the same number of carbons. The C=C bond can open up to make a single bond, allowing them to bond with other atoms
What are the first four alkenes?
Ethene, propene, butene and pentene
Give the general formula for alkenes
CnH2n
Why do alkenes burn with a smoky flame?
Alkenes only combust completely with large amounts of oxygen, which isn’t available, so they tend to undergo incomplete combustion, producing carbon and carbon monoxide
Give the word equation for the incomplete combustion of alkenes
Alkene + oxygen –> carbon + carbon monoxide + carbon dioxide + water (+energy)
What is a functional group?
A group of atoms in a molecule that determine how that molecule typically reacts
What is hydrogenation?
The addition of hydrogen; it can react with the double-bonded carbons to open up the double bond and form the equivalent, saturated, alkane
What happens when steam reacts with alkenes?
Water is added across the double bond and an alcohol is formed
How can ethanol be made industrially from ethene?
Steam is mixed with ethene, passed over a catalyst, reaction mixture is passed from reactor to condensor, ethanol and water have a higher bp than ethene so both condense whilst any unreacted ethene is recycled back. Ethanol can then be purified with fractional distillation
What happens when halogens react with alkenes?
The molecules formed are saturated, with the C=C carbons each becoming bonded to a halogen atom
