ch.12 Flashcards
(42 cards)
what’s the difference between thermal and catalytic cracking
thermal uses high temperatures and high pressures and produces a lot of alkenes to make polymers
while catalytic cracking uses zeolite catalyst at slight pressure and high temp but not as high as thermal
catalytic is better as it is cheaper cuz less pressure and temp needed and the catalyst speeds up the reaction
what problems does soot and carbon monoxide cause when in incomplete combustion
the carbon monoxide sites on haemoglobin molecules in rbc as oxygen molecules sooo oxygen can’t be carried around
use catalytic converters to remove them
carbon soot causes breathing problems
how are oxides of nitrogen produced
when high pressures and temperatures in car engines cause the nitrogen and oxygen atoms from the air to react with each other
how do u form ground level ozone and what problems does it cause
it happens when hydrocarbons and nitrogen oxides react in the presence of sun light
it irritates ppls eyes and aggravates respiratory problems and causes lung damage
what does sulphur dioxide do bad
it dissolves in the moisture and it’s converted in sulphuric acid which causes acid rain
what are two things that can remove co and smog from the car exhausts
oxygenates and catalytic converters
how can sulphur dioxide be moved from power station flue gases using calcium carbonate
powdered calcium carbonate is mixed with water to make alkaline slurry
when the flue gases mix with the alkaline slurry the acidic sulcus dioxide gas reacts with the calcium carbonate to form salt
what’s a free radical
it’s a particle with an unpaired electron
what are the three stages of halogens reacting with alkanes
- initiation reactions
- propagation reactions
- Termination reactions
explain the three stages in the reaction mechanism
— stage one : initiation reaction
free radicals are produced
1. sunlight provided enough energy to break the Cl-Cl bond this is photodissociation
2. the bond are split equally by using UV light and each atom gets to keep one electron and the atom becomes a highly reactive free radicals are
— stage 2 : propagation
1. Cl• attacks a methane molecule
2. the new methyl free radical CH3• can attack another Cl2 molecule
3. the new Cl• can attack another CH4 molecule
— stage 3 : termination
1. if two free radicals join together they make a stable molecule
2. there are heaps of possible termination reactions
what are chlorofluorocarbons CFCs
they’re halogenoalkane molecules where all the hydrogen atoms have been replaced by chlorine and fluorine atoms
what does the ozone layer do
it absorbs UV radiation from sun stopping it from reaching us as UV caused skin cancer and sun burns
how is ozone formed
it’s when an oxygen molecule breaks down to two free radicals cuz of the UV and then it attacks other oxygen to form ozone
how does CFCs create holes in the ozone layer
chlorine free radicals are formed in the upper atmosphere when C-Cl bonds in CFCs are broken down by ultraviolet radiation
these radicals are catalysts
so they react with the ozone to fork an intermediate ClO• and an oxygen molecule
why CFCs now banned
they’re unreactive, non flammable, and non toxic
they cause damage to ozone layer
alternatives were made without chlorine so HFCs hydrofluorocarbons
what halogenoalkane react the fastest and the slowest
iodoalkanes react the fastest while fluoroalkanes react the slowest
the C—F bond is the strongest so it has the strongest bond enthalpg so they undergo nucleus hoc substitution reactions more slowly than other halogenoalkanes
the C—I bond has the lowest bond enthalpy so it’s easier to break this means they’re substituted more quickly
how does fractional distillation work
crude oil is split into fractions when the oil is heated until it is vaporised and then it passed up a tall rawer that is cool at the top as vapour passes up the tower the molecules cool down and condense back into liquids making fractions
what’s fuel and patrol used for
fuel is purified and sold as bottled camping gas
petrol is used to fuel cars and motorcycles and to make chemicals
what’s naphtha and kerosine/ paraffin used for
Naptha— used to make chemicals
Kerosine — it’s a fuel for greenhouse heaters and jet engines
what’s the use of Diesel fuel, fuel and lubricating oil, and bitumen
diesel — fuel for lorrie’s or trains
fuel and lubricating oil — fuel for heating systems of larger buildings or fuel for ships
Bitumen — used for roofing and road surfaces
what’s the order of the fractions
fuel gas
petrol
kerosine
diesel
bitumen
what’s a carbon neutral example
plants photosynthesis using co2 from air
biodiesel releases co2 for plants
plants replant and photosynthesis removing Co2 again
what are adv and disadv of using biofuel
adv.
- biofuels are renewable
- no risks of large scale pollution from exploitation of fossil fuels
disadv
- less food crops may be grown
- rainforests have to be cut down to provide land
- shortage of fertile soils
what are two types of biofuels
ethanol — produced by fermentation of sugars in sugarcane
biodiesel — produced from hydrolysis of vegetable oils
