Alkanes Flashcards
(22 cards)
What is the general formula for an alkane?
CnH2n+2 e.g. C2H6, C3H8
Are they saturated or unsaturated?
Saturated as they contain no C=C bond.
Polar or non-polar?
Non polar
What are the only forces of attraction between neighbouring molecules?
Van der Waals
What happens as chain length increases?
Boiling point increases as the Van der Waals forces of attraction between the molecules increases. The viscosity increases.
What happens when they become branched?
The more branching there is the lower the boiling point, because there are less Van der Waals forces between the molecules as they cannot pack as tightly together.
What is combustion? Complete and incomplete?
Combustion if the chemical reaction of a fuel with oxygen releasing heat and forming oxides.
Complete - Plentiful supply of O2
Incomplete - Limited supply of O2
What does the complete combustion form
Carbon Dioxide and Water
What does the incomplete combustion form
Carbon monoxide and water and soot
What colour do compounds with a high % carbon burn
Smoky orange flame
What colour do compounds with a low % carbon burn
Clean blue
How is the temperature of the earth raised?
Greenhouse gases absorb infrared radiation emitted from the earths surface and reflect it back to earth.
What are the effects of this raised temperature?
Climate change, increased sea levels, melting of polar ice caps and flooding of low-level regions.
What method are used limit the production of greenhouses gases?
1) Removing Sulfur from fuels before combustion
2) Using catalytic converters
3) Scrubbing emissions
4) Using renewable energy resources
What do catalytic converters do?
1) Convert CO to CO2
2) Oxides of nitrogen are converted to N2 and O2
3) Unburnt hydrocarbons are oxidised to CO2 AND H2O
Under what conditions do alkanes react with halogens?
UV light.
If chlorine is mixed methane what will be produced?
Chloromethane, dichloromethane, trichloromethane and tetrechloromethane.
Write out the equations for the reactions listed above.
CH4 + Cl2 –> CH3Cl + HCl etc etc .
What is the mechanism for the monohalogenation of alkanes called? What are the conditions?
Free radical photochemical substitution.
UV light
What is the iniation reaction? Give an example with chlorine. What is it an example of ?
Molecule –> Radicals
UV light
Cl2 ——————-> 2Cl• Homolytic fission
What is the propagation reaction? Continue with the previous example.
Molecule + radical –> radical + molecule
CH4 + Cl• –> CH3• + HCl and
CH3• + Cl2 –> CH3Cl + Cl•
What is the termination reaction? Continue
2 radicals –> Molecule
Cl• + Cl• –> Cl2
CH3• + Cl• –> CH3Cl
CH3• + CH3• –> C2H6
