Why can alkENEs undergo addition reactions?
Because the double carbon bond can open up and bond to atoms of other molecules .
What are the main 3 types of addition reactions WITH?
1) with hydrogen
2) with water
3) with halogens
Describe the addition reaction between alkENEs and hydrogen.
AlkENE + Hydroge—> AlkANE
- Supply a catalyst when we add hydrogen gas.
- Double bond between carbons will break apart so hydrogen will be able to bond to those atoms.
Describe the addition reaction between alkENEs and water/ steam (hydration).
AlkENE + Water —> Alcohol
- Conditions for reaction: catalyst and high temperatures so water would be in the form of water vapour.
- Water breaks down into hydrogen and an OH (functional group for alcohols?) molecule (hydroxide?).
- Double carbon bonds break, hydrogen bonds do a carbon and OH bonds to another carbon.
How do we separate ethanol from unreacted ethane and water?
- Ethene has a low BP so when mixture is cooled down, ethene remains a gas.
- Water and ethanol condense into liquid as mixture is cooled down.
- Water and ethanol separated through fractional distillation.
How are water and ethanol separated through fractional distillation?
- heat mixture of ethanol and water using a Bunsen burner.
- ethanol evaporates first because it has a slightly lower boiling point than water.
- ethanol evaporates up through fractionating column and then condense into a separate beaker.
- water remains in the first flask as it didn’t evaporate.
Describe the addition reaction between alkENEs and halogens (bromine).
AlkENE + Bromine —> DibromoALKANE (colourless solution?)
- No catalyst needed.
General formula for alkENEs?
CnH2n
Describe the complete combustion of alkene?
AlkENE + Oxygen —> CO2 + H2O
Conditions for the hydrogenation of alkENEs?
- Gasses heated to 150C.
- Presence of a nickel catalyst.
How can we make ethanol?
React steam with ethENE over phosphoric acid catalyst.
Why are catalysts used in addition reactions of alkenes?
Using a catalyst allows the reaction to occur at a lower temperature while still maintaining a high rate.
This is important because lower temperatures save energy costs and, in some exothermic addition reactions, can actually increase the yield.
What are alcohols?
- Homologous series of organic componds.
- OH functional group.
- End in “-ol”.
General formula for alcohols?
C(n)H(2n+1)OH
Properties of alcohols (FOS)?
- Flammable
- Oxidised to form carboxylic acids
- Soluble
What does flammability of alcohols mean?
- They can undergo complete combustion:
Alcohol + O2 —> CO2 + H2O
(Remember to balance equation)
What does solubility of alcohols mean?
Dissolve in water to form solutions with a neutral pH.
Uses of alcohols?
- Used as fuels, undergo complete combustion to release lots of energy.
- Used as solvents in industry as they can dissolve things that water can dissolve (particularly hydrocarbons and lipid compounds).
What is ethanol used for?
1) Chemical feedstock to produce other organic compounds.
2) As a biofuel, burnt to produce lots of energy.
3) Used in alcoholic drinks.
How i ethene produced commercially?
Via the addition reactions of ethene (C2H4) with steam (H2O).
What are the conditions required for the addition reactions of ethene with steam to produce ethanol?
High temp- 300C
High pressure- 60 to 70 atm
Catalyst- phosphoric acid
Advantages of reacting ethene with steam to commercially produce ethanol?
- Ethene is cheap.
- Reaction is cheap and efficient.
Disadvantages of reacting ethene with steam to produce ethanol?
- Ethene is made from crude oil which is non-renewable.
- If ethene starts to run out it will become expensive.
What is fermentation?
The anaerobic respiration of sugars by yeast cells to produce ethanol and CO2.
