Organic - 3.2 Alkanes Flashcards
What is a catalytic converter?
A device fitted in a car to reduce the amount of emissions from an internal combustion engine.
What is catalytic cracking?
A type of cracking that takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons.
What is cracking?
A process which involves breaking C-C bonds in alkanes to produce shorter chained alkanes and alkenes.
What is fractional distillation?
A method of separating mixture of substances according to the different boiling points. Common used to separate crude oil into different fractions.
What are hydrocarbons?
Compounds made up of carbon and hydrogen atoms only
What does saturated mean?
Organic compounds are saturated if all the carbon-carbon bonds are single C-C bonds. Alkanes are saturated hydrocarbons.
What is thermal cracking?
A type of cracking that takes place a high pressure and high temperature and produces a high percentage of alkenes.
What is the general formula of alkanes?
CnH2n+2
State the first four alkanes
Methane ethane propane butane
Are alkanes polar and why?
No, because the difference in electronegativity between the carbon atom and hydrogen atom is very small
How are mixtures of alkanes separated?
Through fractional distillation
What is fractional distillation?
The continual evaporation and condensation of a mixture causing the components to separate because of a difference in their boiling points
What is a fraction?
A group of compounds that have similar boiling points and are removed at the same level of a fractionating column
Is a fractionating column hotter at the top or bottom?
Hot at the bottom and cool at the top
What is cracking?
A process where long chain hydrocarbon molecules are broken into shorter chain molecules that are in high demand
What happens in thermal cracking?
Long chain alkanes are heated to a very high temperature high-pressure and in a short time this produces shorter alkanes and rich in alkenes.
What happens in catalytic cracking?
Long chain alkanes are heated under pressure with a zeolite catalyst
What are the conditions and products of thermal cracking?
Temperature = 1000-1200K
Pressure = 700atm
Time = one sec
Catalyst = none
Products = high percentage of alkanes and short chain alkanes
What are the conditions and products of catalytic cracking?
Temperature = 800-1000 K
Pressure = 1-2atm
Time = 2-4secs
catalyst = zeolite
Products = aromatic hydrocarbons and motor fuels
Describe the complete combustion of alkanes
Alkanes burn in oxygen to produce carbon dioxide and water only
Describe the incomplete combustion of alkanes
Alkanes will burn for water and carbon monoxide, which is toxic
What is a catalytic converter?
Reduces the amount of carbon monoxide and nitrous oxide and unburnt hydrocarbons by converting them into less toxic gases
Describe the process that occurs in an internal combustion engine
A small amount of fuel and excess air enters the combustion chamber.
The mixture is then compressed and ignited with a temperature spark .
Mixture then burns explosively forcing movement of the engine.
The products exit via the exhaust
Why can sulphur dioxide be removed from flue gases by calcium oxide and calcium carbonate?
They neutralise the acidic sulphur oxide to form calcium sulphate which is used for construction
What happens in the initiation step of the reaction between methane and chlorine?
The molecules of chlorine absorbed energy supplied by UV light and the chlorine covalent bond breaks.
Each atom from the bond leaves with one electron from the shared pair of electrons.
Two chlorine atoms are formed and each atom has an unpaired electron in the outer shell, these are called free radicals are are extremely reactive.
Cl2 -> Cl• + Cl•
What happens in the propagation step of the reaction between methane and chlorine?
The highly reactive chlorine free radicals react with the methane molecules forming hydrogen chloride gas and a methyl free radical.
The meatball free radical reacts with a second chlorine molecule forming chloromethane and another chlorine free radical .
Discontinuing process of producing free radicals is known as a chain reaction .
Cl• + CH4 -> HCl + •CH3
•CH3 + Cl2 -> CH3Cl + Cl•
What happens in a termination step of the reaction between methane and chlorine?
In order for the reaction to stop to the radicals must collide and react for a molecule.
Cl• + Cl• -> Cl2
Cl• + •CH3 -> CH3Cl
•CH3 + •CH3 -> C2H6
What is the reaction between methane and chlorine called?
A free radical substitution reaction
What is the process called that involves the breaking of a covalent bond to produce two free radicals?
Homolytic fission
What process occurs in an internal combustion engine?
Step 1) A small amount of fuel is mixed with a large excess of air is drawn into a combustion chamber.
Step 2) The mixture is compressed and ignited with an extreme temperature spark.
Step 3) The mixture burns explosively forcing movement of the engine parts.
Step 4) The products of combustion exit via the exhaust.
What are the equations for the reactions that take place in an internal combustion engine?
nitrogen + oxygen -> nitrogen (II) oxide
N2(g) + O2(g) -> 2NO(g)
nitrogen + oxygen -> nitrogen (IV) oxide
N2(g) + O2(g) -> 2NO2(g)
sulfur + oxygen -> sulfur dioxide
S + O2(g) -> SO2(g)
What is a catalytic converter?
A catalytic converter reduces the amount of carbon monoxide, nitrogen oxides and unburnt hydrocarbons released into the air from an internal combustion engine, by converting them into less toxic gases.
What are the catalysts used in a catalytic converter?
Platinum and rhodium catalysts.
What are the equations for the reactions that take place in catalytic converters to produce less polluting products?
nitrogen (II) oxide + carbon monoxide -> carbon dioxide + nitrogen
2NO(g) + 2CO(g) -> 2CO2(g) + N2(g)
octane + nitrogen (II) oxide -> carbon dioxide + nitrogen + water
C8H18(g) + 25NO -> 8CO2(g) +12.5 N2(g) + 9H2O(g)
