Alkanes Flashcards
What are the conditions for thermal cracking
450 - 750*C
70 atm
What are the major products in thermal cracking
mixtures of products containing high proportions of alkenes
What are the conditions for catalytic cracking
500*C
1-2 atm
zeolite catalyst (large surface area)
What are the major products of catalytic cracking
produces high proportions of branched alkanes and aromatic hydrocarbons e.g. benzene
How does a catalyst increase the rate of reaction
reactants adsorb onto surface of catalyst
weakens bonds in the molecules which lowers the activation energy
increases rate of reaction
Describe the set up of apparatus for cracking in the lab
horizontal test tube containing mineral wool soaked in parafin and a zeolite catalyst
tube from test tube into upside down submerged test tube in a beaker
bunsen burner underneath horizontal test tube
What is reforming
the processing of straight chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons for efficient combustion
- done to reduce knocking by increases the octane number
What are the conditions for reforming
around 500*C
around 20 atm
mixture of platinum and aluminium oxide catalyst
How is carbon monoxide formed and what problem does it cause
incomplete combustion of fuels containing C
toxic - binds to haemoglobin in lungs
How is soot formed and what problem does it cause
incomplete combustion of fuels containing C
can cause respiratory issues, global dimming
How is sulfur dioxide formed and what problem does it cause
combustion of S containing compounds in fuel
causes acid rain - makes soil too acidic
How are oxides of nitrogen formed and what problems can they cause
Reaction of nitrogen with oxygen in the air at very high temperatures ( in engines and furnaces )
causes acid rain, can cause respiratory issues
How can we reduce the problem caused by carbon monoxide
ensure a good supply of oxygen when burning fuels
- use a catalytic converter
How can we reduce the problem caused by soot
ensure a good supply of oxygen when burning fuels
How can we reduce the problem caused by sulfur dioxide
remove S from fuel before burning
- flue gas desulfurisation
How can we reduce the problem caused by oxides of nitrogen
use catalytic converters in cars
What does a catalytic converter do
uses a rhodium catalyst to convert harmful products such as CO and NOx into more stable products such as CO2 or H2O
What mechanism occurs in the reaction between halogens and alkanes
free radical substitution
- produces a haloalkane
What happens in the initiation stage of free radical substitution
homolytic fission
the halogen splits into two free radicals in the presence of UV light
What is a free radical
an atom or molecule that has an unpaired election
- makes them highly reactive
What happens in the propagation stage of free radical substitution (methane and chlorine)
Cl. + CH4 -> HCl + CH3.
CH3. + Cl2 -> CH3Cl + Cl.
What happens in the termination stage of free radical substitution
2 radicals react together to end the reaction
How can we reduce multiple substitution of halogens in free radical substitution
use an excess of the alkane
- this increases the change of a halogen radical from colliding with a alkane rather than a product molecule
What are the two types of biofuels
biodiesel
bioalcohol
