Cracking: Alkenes

why are short term hydrocarbons more useful and valuble?

more flammable and burn easier,

have a larger energy output

what is cracking used for?

to split long chain hydrocarbons into short chain

2 types of cracking?

Thermal and catalytic

conditons required for thermal cracking to take place?

high temperatures (400-900), high pressures (7000kPa)

why do we need high temperatures for thermal cracking?

C-C bonds have high bond enthalpy, cracking requires lots of energy

products of thermal cracking?

1/1+ alkenes and linear, 1 short chain alkane

what are the alkenes produced in thermal cracking mainly used for?

plastics

how to write an equation to deduce products of thermal cracking?

1 write an equation with info given

2 work out type of hydrocarbon missing

3 calculate the difference between the atoms in the products and reactants

4 write out equation

why is there only 1 alkane produced in thermal cracking?

producing more is not viable

difference between thermal and catalytic cracking?

catalytic uses a zeolite catalyst

is zeolite a heterogenous or homogenous catalyst?

heterogenous, it is solid whilst the reactants are liquid

conditions required for catalytic cracking?

high temperature (450+), moderate pressure, zeolite catalyst

why does catalytic cracking use a lower temperature than thermal?

catalyst provides an alternative reaction pathway, increasing rate, so theres less need for higher temp's

products of catalytic cracking?

1 or more branched or cycloalkanes, aromatic compounds

what can the branched alkanes produced in catalytic cracking be used for?

fuels

advantages of thermal cracking?

• produces valuble short chain alkanes

• produces alkenes, used for plastics

• produces mainly short chain alkanes

advantages of catalytic cracking?

• produces valuable short chain alkanes

• catalyst makes it cheaper and easier

• mainly branched alkanes produced, used for fuel

limitations of thermal cracking?

expensive process due to high temperature and pressure

limitations of catalytic cracking?

zeolite is expensive and needs to be replaced often