2.5 Flashcards
What is a fossil fuel
Fossil fuel is one that is
derived from organisms that
lived long ago.
Advantages of fossil fuels
- variety available - each use can be matched to appropriate fuel
- available at all times
- widely available
Disadvantages of fossil fuels
- non-renewable
- produces CO2 on combustion - greenhouse gas
- combustion of fossil fuels that contain sulfur and nitrogen leads to acid rain
- carbon monoxide is formed during incomplete combustion
What is a non-renewable source
Cannot be reformed in a reasonable timescale
What is acid rain and its environmental effect
Rain with lower than expected pH
Combustion of fossil fuels that contain sulfur and nitrogen produce the dioxides which react with water to form sulfuric acid and nitric acid
Contains sulfuric acid and nitric acid
Damages buildings, vegetation and aquatic life
Health issues for people with breathing difficulties
Why are alkanes generally unreactive
Non-polar and dont contain multiple bonds
What is combustion
When alkanes burn and react with oxygen in exothermic reactions and are used as fuels
Complete combustion
Combustion that occurs with excess oxygen
Sufficient oxygen is present
Carbon dioxide and water are produced
Incomplete combustion
Combustion that occurs with insufficient oxygen
Carbon monoxide and water is formed
Less energy than complete combustion
Why is carbon monoxide toxic
Can inhibit transport of oxygen through the body as it combines with haemoglobin
What is halogenation
Reaction between organic compound and any halogen
What are the two important reactions of alkanes
Combustion and halogenation
What are the 3 mechanisms of halogenation
Initiation
Propagation
Termination
What is initiation in halogenation
Reaction that starts the process
Homolytic bond fission of chlorine to produce 2Cl•
Energy needed to break the bond is provided bu uv light
What is propagation in halogenation
Reaction by which the process continues/grows
Radicals take part as they’re so reactive
Starts with a radical then produces one so that the chain reaction occurs
Cl• + CH4 —>
CH3• + HCl
CH3• + Cl2 —>
CH3Cl + Cl•
What is termination in halogenation
The reaction that ends the process
Chain reaction continues until 2 radicals meet
CH3•+Cl• —> CH3Cl
Overall equation of halogenation
C2H6 +Cl2 —> C2H5Cl + HCl
What is a pi bond
One formed by the sideways overlap of p electrons
Double bond
High electron density above and below the plane of the molecule
What makes alkenes susceptible to attach by an electrophile
The pair of electrons in the pi orbital
What kind of bond fission is involved in electrophilic addition
Heterolytic
What is an addition reaction
Reaction in which reagents combine to give one product
What is shown by the curly arrows of this electrophilic addition
Movement of the electron pair
If the attacking species is non-polar during electrophilic addition, how is a dipole induced
By the negative charge of the pi bond
Test for alkenes
Reaction with bromine
• brown colour of bromine changes to colourless
• use of aqueous bromine as it is safer
Reaction with potassium manganate (VII)
Reaction with acidified potassium manganate
• purple manganate(VII) is decolorised
Why, on the addition of HBr to alkenes , 2-bromopropane is the major product and not 1-bromopropane
It has greater stability of the 2• carbonation compared with the 1• carbonation
Which type of carbocation
2•
Which type of carbocation
1•
What is polymerisation
Joining of a very large number of monomer molecules to make a large polymer molecule
What is a monomer
Small molecule that can be made into a polymer
What is a polymer
Large molecules made by joining many monomers
What kind of molecules undergo addition polymerisation and why
Alkenes and substituted alkenes
They have a double bond which is used to join the monomers and nothing is eliminated
Think of the polymer that would come of this monomer
What is the name of the polymer of ethene
Poly(ethene)
Properties of poly(ethene)
Unreactive and flexible
Can be used to make plastic bags
Why do polymers have a huge variety of uses
The properties of polymers can be altered by using substituted alkenes as the monomer
Properties of poly(propene)
Rigid
Used in food containers and kitchen equipment
Properties of poly(chloroethene) or PVC
Flexible
Water pipes, waterproof clothes and insulating covering for electrical cables
Properties of poly(phenylethene) or polystyrene
Hard - gives strength and rigidity
Made into an insulator by making holes in the structure
Which polymer
Poly(propene)
Which polymer
Poly(chloroethene)
Which polymer
Poly(phenylethene)
Why is CO2 bad for the environment
Absorbs infrared radiation from earth, then it emits it in all directions
Some of the radiation goes back towards the earth’s surface
Causes the surface’s temperature to rise
Can lead to rising sea levels and changes to crop stability
Why are radical reactions hard to control
Further substitution can occur
A mixture of products may be formed
Unsatisfactory method of getting a high yield of a specific halogenoalkane
Can be largely avoided by limiting the amount if the halogen
Name of this reaction
Electrophilic addition
Monomer or repeating unit
Monomer
Monomer or repeating unit
Repeating unit
