Alkanes and Alkenes

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What are alkanes?
Saturated hydrocarbons with single bonds only
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How reactive are alkanes?
Very unreactive
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What are alkanes used for?
Fuels and lubricants
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What is the general formula for alkanes?
CnH2n+2
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What are unbranched called?
Chains
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What is the C-C-C bond angle?
109.5
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What is the general formula for ring alkanes?
CnH2n
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What is the polarity of alkanes?
Almost non polar because the electronegativities of carbon and hydrogen are so similar
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What is the trend in boiling points for alkanes?
Increase in chain length, increasing van de waals forces
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What state are small chains in at room temperature?
Gases
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Why do branched chains have lower melting points than straight chains?
They aren't as closely packed together, the van de waals are less effective
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Are alkanes soluble?
Insoluble in water, water molecules are held together by hydrogen bonds which are much stronger than van de waals
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What is the process of separating fractions that boil at different temperatures?
Fractional Distillation
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Why are fractions cracked?
To make products that are in high demand
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What are the 2 useful results of cracking?
1. Shorter more useful chains 2. Some products are alkenes
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What conditions are needed for thermal cracking?
High temperatures, high pressure
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How does thermal cracking work?
C-C bonds break in a way so one electron from a pair goes to each carbon atom, there are not enough hydrogens to produce two alkanes, so an alkene is produced
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What are the conditions for catalytic cracking?
lower temperatures and pressures
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What catalyst is used in catalytic cracking?
Zeolite, silicon dioxide, aluminium oxide
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What's the structure of zeolite catalysts?
Honeycomb structure with an enormous structure
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Name examples of alkane fuels?
Methane(natural gas, Propane(camping gas), Butane(calor gas), Petrol, Paraffin
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What are the polluting gases from fuels?
Carbon monoxide, nitrogen oxides, sulfur dioxide, water vapour, carbon, carbon dioxide
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How is nitrogen oxide produced in a petrol engine?
N2 + O2-------->2NO
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When in nitrogen oxide produced?
When ignited by a spark or high temperature
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How is sulfur removed?
Calcium oxide to absorb sulfur dioxide, this produces gypsum
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What is the process of removing sulfur called?
Flue gas desulfurisation
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What is the structure of a catalytic converter?
Honeycomb made of a ceramic material coated with platinumWhat i and rhodium metals
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What is the reaction in a catalytic converter?
2CO+2NO----> N2 + 2CO2
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What are sun spots?
Magnetic zones that appear on the sun as dark spots and appear to increase sun energy output
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What are alkenes?
Unsaturated hydrocarbons with at least one double bond
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What are the end uses of alkenes?
Polymers
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What is the general formula for alkenes?
CnH2n
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What can't C=C bonds rotate?
There is a p orbital on each carbon, these 2 orbitals overlap to form one single orbital with a cloud of electron density above and below the single bond,pi orbital, its
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What two isomers can alkenes form?
Position and geometrical
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What are position isomers?
The double bond changes position
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What is geometrical isomerism a form of?
Stereoisomerism
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Why is an alkene called a Z?
When CH3 groups are on the same side of the double bond
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Why is an alkene called an E?
When the CH3 groups are on opposite sides
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Why are alkenes reactive?
The double bond forms an electron rich area in the molecule which can easily be attacked by positively charged reagents
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What is electrophile?
Electron liking
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What are most of the reaction alkenes undergo?
Electrophile additions
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What happens in a electrophillic addition reaction?
The electrophile is attracted to the double bond, electrophiles are positively charged and accept a pair of electrons, a positive ion is formed, a negatively charged ion forms a bond with positive ion
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Examples of hydrogen halides?
HCl,HBr, HI
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What's an alkene bonded with a hydrogen halide called?
Haloalkane
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What a positive inductive effect?
Alkyl groups have a tendency to release electrons
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What's a carbocation?
Positive ion
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What effect does the positive inductive effect have?
Stabilise positive charge of carbocation, the more alkyl groups attached the more stable the carbocation is
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When alkenes react with halogens where do they join?
Across the double bond
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What do halogen molecules act as when they react with alkenes?
Electrophiles, halogen molecules has an instantaneous dipole and the positive end of the dipole is attracted to the electron rich double bond
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What are the 2 steps that take place when halogens react with alkenes?
1. Formation of the carbocation by electrophile addition 2. Rapid reaction with a negative ion
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How do you test for a double bond?
Add bromine water(reddish brown) to an alkene, it will turn colourless
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Describe the reaction sulphuric acid and alkenes?
Sulfuric acid joins at the double bond, occurs at room temp and is exothermic
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What are polymers?
Long chains molecules made from joining small monomers
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What reaction is used to make polymers from alkenes?
Addition Polymerisation
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How is low density poly(ethene)made?
High pressure and temp via a free radical mechanism, produces a polymers with chain branching, quite flexible e.g plastic bags
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How is high density poly(ethene) made?
Room temp and pressure and uses a Ziegler-Natta catalyst, less chain branching, packed together e.g. milk crates
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What are the problems with plastics?
Not broken down quickly, not biodegradable, plastic litter, landfill
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What is mechanical recycling?
Separating different types of plastics, washed and ground up into small pellets, they are then melted and remoulded
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What is feedstock recycling?
Plastics are heated to a temp that will break polymer bonds and make monomers, than can be made into new plastics
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What's the problems with recycling?
Plastics can be heated only a number of times as the chains break and become shorter, the plastics properties become degraded.
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Other cards in this set

Card 2

Front

How reactive are alkanes?

Back

Very unreactive

Card 3

Front

What are alkanes used for?

Back

Preview of the front of card 3

Card 4

Front

What is the general formula for alkanes?

Back

Preview of the front of card 4

Card 5

Front

What are unbranched called?

Back

Preview of the front of card 5
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