Alkanes Flashcards
What are the reactivity of alkanes like?
Very unreactive
What can alkanes be used for?
Starting material for other reactions
Fuels
Lubricants
What is the main source of alkanes?
Crude oil
What is the general molecular formula of ringed alkanes?
CnH2n
Describe the polarity of alkanes
Almost non-polar because the electronegativities of carbon and hydrogen are so similar
What intermolecular forces are present in alkanes?
Wan der Vaals forces
Describe the boiling points of alkanes
Boiling point increases as the carbon chain length increases due to more electrons and stronger Van Der Waals forces
What is the state of alkanes with a chain length of 0-5 carbons?
Gas
What is the state of an alkane with a chain length of 5-18 carbons?
Liquid
What is the state of an alkane with a chain length of >18 carbons?
Solid
Why do branched alkanes have a lower boiling point than straight chained alkanes?
They cannot pack as close together as straight chained alkanes can which makes the Van der Waals forces less effective
Describe the solubilities of alkanes
Insoluble in water because the hydrogen bonds that hold water together are more strong than the Wan der Waals forces that hold together alkanes
They do mix relatively well with non-polar liquids
Why are longer chain alkanes cracked?
They’re not as economically valuable as shorter chained alkanes and alkenes
What are the conditions for thermal cracking?
Heating alkanes to a high temperature - 700-1200K
High pressure, up to 700KPa
Outline the process for thermal cracking
C-C bonds break homolytically, producing two free radicals
Free radicals react to produce a range of shorter chained compounds
How is further decomposition prevented in the thermal cracking of compounds?
The conditions are kept for a short time period
Outline the conditions for catalytic cracking with the catalyst that is used
Lower temperatures - 720K
Lower pressures - more than atmospheric
zeolite catalyst - consisting of silicon dioxide and aluminium oxide
What structure do zeolite catalysts have?
Honeycomb structure with a large surface area
Acidic
Outline the practical procedure for catalytic cracking
Mineral wool soaked in light paraffin is at the end of a horizontal test tube with a beaker in it
Aluminium oxide catalyst is in the centre with heat being applies
Tubbing goes to an upside down test tube in a bucket filled with water
Mixture produced decolourises bromine water due to the presence of a double bond in the alkenes produced
Outline the effects of the polluted gases that are produced via the combustion of burning hydrocarbons
-CO, poisonous gas produced via incomplete combustion
- Nitrogen oxides, NO, NO2 & N2O4 are produced when there is enough energy for nitrogen and oxygen to combine in the air
- N2 (g) + O2 (g) → 2NO (g)
- This happens in petrol engines at high temperatures, these oxides may react with water vapour and oxygen in the air to produce nitric acid
- They’re therefore contributors to photochemical smog and acid rain
- Sulfur dioxide is another contributor to acid rain
- Produced from sulfur containing impurities in crude oil
- Oxide combines with oxygen and water in the air to produce sulfuric acid
-Carbon particles, particulates, can exacerbate asthma and cause cancer
- Unburnt hydrocarbons can also enter the atmosphere and and are greenhouse gases
- They also contribute to photochemical smog
- Carbon dioxide is a greenhouse gas
- Water vapour is a greenhouse gas
Outline flue gas desulfurisation
- Gases that leave power stations are called flue gases
- Many flue gasses contain SO2
1) A slurry of calcium oxide and water is sprayed onto the flue gas which reacts with the calcium oxide and water to form calcium sulfite, which can then be further oxidised to calcium sulphate (gypsum)
- CaO (s) + 2H2O (l) + SO2 (g) + 1/2 O2 (g) → CaSO4 (s) + CO2 (g)
OR
-Use calcium carbonate
CaCO3 (s) + 1/2O2 (g) + SO2 (g) → CaSO4 (s) + CO2 (g)
Write the equation for the formation of sulfuric acid from sulfur dioxide
SO2 (g) + 1/2 O2 (g) + H2O (l) → H2SO4 (l)
What is the structure of a catalytic converter?
A honeycomb structure made of ceramic material coated with platinum and rhodium metals (these are the catalysts)
Write the general equation for the process that occurs inside a catalytic converter alongside an equation using examples
Write a third equation in the case of carbon monoxide
Hydrocarbons + nitrogen oxide → nitrogen + carbon dioxide + water
C8H18 + 25NO → 12 1/2N2 + 8CO2 + 9H2O
2CO (g) + 2NO (g) → N2 (g) + 2CO2 (g)
Where do the reactions take place in catalytic converters?
On the surface of the catalytic converter on the layers of platinum and rhodium
Write the equations for the depletion of the ozone layer
Cl2 → 2Cl•
Cl• + O3 → ClO• + O2
ClO• + O3 → 2O2 + Cl•
Write the overall equation for the depletion of the ozone layer
2O3 → 3O2
