14.2 Functional Group Chemistry Flashcards
What type of carbon bonds do compounds in the alkane group have?
only single carbon bonds
What is the alkane group?
A homologous series of hydrocarbon compounds with only single carbon bonds, there are no C=C bonds present
What is the general formula of alkanes?
CnH2n+2
What type of hydrocarbons are alkanes?
Alkanes are classified as saturated hydrocarbons
What does it mean if an alkane is saturated?
all the carbon bonds in alkanes are single bonds
What colour are alkanes?
They are colourless compounds
What changes across the alkane group?
have a gradual change in their physical properties as the number of carbon atoms in the chain increases
Are alkanes reactive?
Alkanes are generally unreactive compounds
What reactions can alkanes undergo? (3)
- they undergo combustion reactions
- can be cracked into smaller molecules
- react with halogens in the presence of light
What fossil fuel is an alkane?
Methane is an alkane and is the major component of natural gas
What are the first 3 alkanes?
methane
ethane
propane
What is a substitution reaction?
In a substitution reaction, one atom is swapped with another atom
With what group do alkanes react with in a substitution reaction?
Alkanes undergo a substitution reaction with halogens
What condition must be present for a substitution reaction between halogens and alkanes to occur?
the presence of ultraviolet radiation
Word equation for methane and bromine
Methane + Bromine → Bromomethane + Hydrogen Bromide
Chemical Equation for methane and bromine
CH4 + Br2 → CH3Br + HBr
What is the alkene group?
A homologous series of hydrocarbon compounds with carbon-carbon double bonds (C = C)
What is the general formula for the alkene group?
CnH2n
What chemical characteristic do ALL alkenes have?
All alkenes contain a double carbon bond, which is shown as two lines between two of the carbon atoms
What is the double carbon bond present in alkenes known as?
This is the alkene functional group and is what allows alkenes to react in ways that alkanes cannot
What type of hydrocarbons are alkenes?
Compounds that have a C=C double bond are also called unsaturated compounds
Why is catalytic cracking used?
Although there is use for each fraction obtained from the fractional distillation of crude oil, the amount of longer chain hydrocarbons produced is far greater than needed
What is converted into what during catalytic cracking?
A process called catalytic cracking is used to convert longer-chain molecules into short-chain and more useful hydrocarbons
What is a product of cracking alkenes?
Alkenes and hydrogen are produced from the cracking of alkanes
What 2 alkenes are most commonly used in cracking and what do they produce?
Kerosene and diesel oil are often cracked to produce petrol, other alkenes and hydrogen
- What is the first step for catalytic cracking?
catalytic cracking
Fractions containing large hydrocarbon molecules are heated at 600 – 700°C to vaporise them
- What happens to the hydrocarbon vapours?
catalytic cracking
Vapours will then pass over a hot catalyst of silica or alumina
- Why are the vapours passed over a hot catalyst? What reaction occurs?
catalytic cracking
This process breaks covalent bonds in the molecules, causing thermal decomposition reactions
- What happens as a result of these reactions?
catalytic cracking
As a result, cracking produces smaller alkanes and alkenes.
The molecules are broken up in a random way which produce a mixture of alkanes and alkenes
- What are the optimum conditions for catalytic cracking?
catalytic cracking
Hydrogen and a higher proportion of alkenes are formed at temperatures of above 700ºC and higher pressure
Do alkanes and alkenes have the same molecular structures?
NO
they have different ones
What is the difference between alkanes and alkenes referring to their carbon bonds?
All alkanes are saturated and alkenes are unsaturated
What chemical property allows us to differentiate between alkanes and alkenes?
The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot
- What substance can be used to differentiate between alkanes and alkenes?
differentiating between alkenes and alkanes
bromine water
- What is bromine water?
differentiating between alkenes and alkanes
Bromine water is an orange coloured solution of bromine
- What will happen when bromine water is shaken with an alkane? Why?
differentiating between alkenes and alkanes
When bromine water is shaken with an Alkane, it will remain as an orange solution as alkanes do not have double carbon bonds (C=C) so the bromine remains in solution
- What will happen when bromine water is shaken with an alkene? Why?
differentiating between alkenes and alkanes
when bromine water is shaken with an alkene, the alkene will decolourise the bromine water and turn colourless as alkenes do have double carbon bonds (C=C)
- Why do the double carbon bonds decolourise the bromine water?
differentiating between alkenes and alkanes
The bromine atoms add across the C=C double bond hence the solution no longer contains the orange coloured bromine
- What is this decolorisation reaction called?
differentiating between alkenes and alkanes
This reaction between alkenes and bromine is called an addition reaction
- What is an addition reaction?
differentiating between alkenes and alkanes
A reaction in which a simple molecule adds across the carbon-carbon double bond of an alkene
- How are addition polymers formed? What makes them up?
addition polymerisation
Addition polymers are formed by the joining up of many small molecules called monomers
- In what monomers does addition polymerisation take place?
addition polymerisation
Addition polymerisation only occurs in monomers that contain C=C bonds
- What happens to the double carbon bonds during addition polymerisation? What new bonds are formed?
addition polymerisation
One of the bonds in each double bond breaks and forms a bond with the adjacent monomer
- What is an example of a polymer synthesised from alkene monomers? What is it made of?
addition polymerisation
A common example is poly-ethene (polythene) which is the addition of many ethene monomers
What is an example of an addition reaction?
ethene + bromine
What is formed between the addition reaction of ethene and bromine?
ethene + bromine –> 1,2-dibromoethane
- With what element do alkenes react to form alkanes?
hydrogenation reactions
Alkenes also undergo addition reactions with hydrogen in which an alkane is formed
- What is the reaction between alkenes and
hydrogen called?
h r
These are hydrogenation reactions