3.2 Alkanes Flashcards
Saturated
Compounds with single bonds only
Hydrocarbons
Compounds with carbon and hydrogen only
General formula
CnH2n+2
Factors affecting boiling point of alkanes
Chain length
Number of branches
Trend of boiling point with increasing carbon chain length
Boiling point increases
More molecules
Strength of induced dipole dipole between molecules gets stronger
Trend of boiling point with increasing number of branches
Boiling point decreases
More branches
More surface contact area
Induced dipole dipole between molecules stronger
Crude oil
Mixture of hydrocarbons with different chain lengths
Fraction
Mixture of compounds with similar BP and size of molecules
Features of fractional distillation
- Crude oil heated to vaporise and enters column
- Hydrocarbons have different BP, depending on size, Mr and chain length
- Cooler at the top and hotter at the bottom
- Larger molecules condense at the bottom
Fractions in column
Gasoline
Naphtha
Paraffin
Diesel
Lubricating oil
Bitumen
Purpose of cracking
To make alkenes and shorter chain molecules
Thermal cracking conditions
High temp : 700-1200K
High pressure : 7000KPa
Products of thermal cracking
One alkane
Many alkenes
Catalytic cracking conditions
High temp : 720K
Slight pressure : 100KPa
Catalyst: Zeolite
Products of catalytic cracking
High percentage of branched alkanes and cycloalkanes
Complete combustion of nonane
C9H20 + 14O2 –> 9CO2 + 10H2O
Incomplete combustion of dodecane to produce gases only
C10H22 + 21/2O2 –> 10CO + 11H2O
Incomplete combustion of but-1-ene to produce a solid
C4H8 + 2O2 –> 4C + 4H2O
What is carbon dioxide
Greenhouse gas
What is water
Greenhouse gas
What is carbon monoxide
Poisonous gas
What does solid carbon do
Damages the lungs
Equation for the formation of acid rain
SO2 + 1/2O2 + H2O –> H2SO4
Equation for the formation of sulphur dioxide
S + O –> SO2
Equation of nitrogen dioxide dissolving in rainwater
4NO2 + 2H2O + O2 –> 4HNO3
What is a catalytic converter
A honeycomb structure made of platinum and rhodium
What does a catalytic converter do
Converts some of the harmful gases in a car exhaust into less harmful gases
Increases the surface area, increasing the rate of reactions
What are the problems with unburned hydrocarbons
They are toxic and ca n. cause cancer if breathed in
Desulfurisation
Acidic sulphur dioxide neutralised by alkali
Removal of carbon and nitrogen monoxide equation
2NO + 2CO –> N2 + 2CO2
