DF 2.0 Flashcards
catalysis, optical isomerism
describe how heterogenous catalysts work
reactants are adsorbed onto the catalyst surface and bonds are weakened
bonds break in the reactant molecules and new bonds form between reactants to form the products
the product desorbs/diffuses away from catalyst surface
catalyst poisoning
a substance that stops a catalyst functioning properly
describe the process of catalyst poisoning in heterogenous catalysis
poison molecules are adsorbed more strongly onto the catalyst surface than reactant molecules
the catalyst cannot catalyse a reaction with the poison so becomes inactive
i.e why leaded petrol cannot be used in cars with a catalytic converter bc lead is strongly adsorbed onto the surface
why does catalyst poisoning mean it is not possible to replace costly metals in CCs with cheaper metals
cheaper metals are vulnerable to poisoning by trace amounts of sulfur dioxide present in car exhaust gases so a new converter will need to be bought which is very expensive
how can the surface of a catalyst be regenerated once poisoned
if carbon is covering the surface, the catalyst can be recycled through a separate container where hot air is blown through
the oxygen in the air converts the carbon to carbon dioxide and cleans the catalyst surface
describe how to determine the number of optical isomers a molecule has
calculate the number of chiral centres, then use 2n-1 where n = the number of chiral centres
effects of PS smog
haziness, reduced visibility, enhance respiratory issues
how is PS smog formed
when primary pollutants are acted upon by sunlight to produce secondary pollutants
how is acid rain formed
sulfur dioxide reacts with water in the atmosphere to form sulfuric IV acid
which is oxidised to sulfur trioxide in the stratosphere
which reacts with water to form sulfuric VI acid
what are the effects of acid rain
breathing difficulties, corrodes limestone buildings, kills forests and life in lakes
what is the role of a catalytic converter
they speed up the three naturally occurring reactions to remove pollutants, the reactions would otherwise occur too slowly due to the conditions of the exhaust
how is carbon monoxide, hydrocarbons and nitrogen monoxide removed from the exhaust by a catalytic converter
2CO + O2 -> 2CO2
C7H16 + 11O2 -> 7CO2 + 8H20
2NO + CO -> N2 + 2CO2
what catalytic converters are available in diesel engines
reduction of any NOx to nitrogen would be impossible because any reducing agent would be oxidised by the higher concentration of oxygen, therefore diesel engines contain oxidation catalysts to turn CO to CO2 and HCs to CO2 + H2O
how else can pollutants be reduced in diesel engines
particulates removed by diesel particulate filters
regeneration is done by increasing the temperature at certain times in order to increase fuel consumption
nitrogen oxides can be reduced by recycling some of the exhaust gases through the cylinder lowering the temperature and thus the amount of NOx formed
alternatively a reagent like ammonia is used in the presence of a catalyst
4NO + 4NH3 + O2 -> 4N2 + 6H2O
source of ethanol
fermentation of carbohydrate crops
evaluate ‘ethanol is carbon neutral’
CO2 produced in fermentation/burning CH3OH matches that absorbed in the growing plant.
however energy is used to produce and distribute the CH3OH, producing more CO2 if from fossil fuels
also land could be otherwise used for producing food instead of crop fermentation
source of biodiesel
chemically reacting fats and oils with an alcohol to produce fatty acid esters (trans-esterification)
advantages of biodiesel over diesel
made from waste oil instead of fossil fuel based oil
arguably carbon neutral
some diesel vehicles can run on pure biodiesel
biodegradable if spilled
no sulfur so reduces oxides of sulfur in emissions
less particulates, CO and HCs than petrol and diesel
two other examples of biofuels
green diesel and biogas (methane derived from animal manure etc)
disadvantage of biodiesel over diesel
produces more nitrogen oxides than conventional fossil fuels
adv of hydrogen as fuel
renewable, made by electrolysis of water
stored and sent down pipelines, used in internal combustion/fuel cells to generate electricity
produces no CO2, CO or HCs when burnt
disadv of hydrogen as a fuel
production from water depends on use of electricity from fossil fuel power
less energy dense than petrol
oxides of nitrogen still produced
what does hydrogen produce and not produce when burned as fuel in a car engine
produces oxides of nitrogen, does not produce particulates, carbon monoxide or sulphur dioxides
