Chemistry science axs

Large hydrocarbon molecules can be broken down into smaler molecules by a process called cracking

cracking is done in two ways:

-by heating a mixture of hydrocarbon vapours and steam to a very high tempreture

-by passing hydrocarbon vapours over a hot catalyst

during cracking thermal decompostion reactions produce a mixture  of smaller  molecules

these alnalkanes with smaller molecues are more useful  as fuels

these are called alkenes 

alkenes are unsaturated hydrocarbons because they contain fewer hydrogen atoms than alkanes with the same number of carbon atoms

alkenes have a double bonds between two carbon atoms this makes them more reactive than alkanes, alkenes react with bromine water turning it from orange to colourless

plastics are made of polymers 

polymers are made from many molecules joined together 

the small molecules used to make polymers are called monomers

molecules can join together to make polyethene

new polymers are being developed all the time

polymers are designed to have properties that make them specailly suited for certain uses

we are now recycling more plastics and finding new uses 

smart polymer is a material used for stiching wounds that changes shape when heated to body tempreture

many polymers are not biodegradable

non-biodegradable plastics cause unsightly rubbish, can harm wildlife and take up space in landfill sites

biodegrable plastics are decomposed by the action of mocrooganisms in soil

making plastics with starch granules in their structure helps the microorganisms break down a plastics

we can make biodegradable plastics from plant material such as cornstarch

ethanol has a formuler of 

ethanol can  be made by fermenting sugar using enzymes in yeast

ethanol can also be made by hydration of ethene with steam in the presence of a catalyst

using ethene to make ethanol needs non-renewable crude oil whereas fermenation uses renewable plant material