DF5

Question 1

Cracking

Answer 1

any reaction in which a large molecule is made into smaller molecules

Question 2

Reasons for cracking

Answer 2

to meet the demand of petrol, to get other desirable chemicals eg. alkenes

Question 3

Unsaturated

Answer 3

a compound not containing the maximum number of hydrogen because it contains double/triple bonds

Question 4

Catalyst

Answer 4

increases the rate of chemical reaction but can be recovered chemically unchanged at the end

Question 5

Physical changes of a catalyst

Answer 5

may sometimes be changed physically, eg. solid catalyst begins to crumble, this suggests the catalyst is taking part in the reaction but is being regenerated

Question 6

Homogeneous catalysis

Answer 6

when the reactant and catalyst are in the same physical state

Question 7

Heterogeneous catalysis

Answer 7

when the catalyst and reactant are in different physical states

Question 8

Heterogeneous catalysis; process

Answer 8

reactants are adsorbed onto the catalyst surface,
bonds are weakened,
bonds break and new bonds form,
product diffuses away from catalyst surface leaving it free to adsorb fresh reactants

Question 9

Poisoned catalysts; process

Answer 9

poison molecules are adsorbed strongly to the catalyst surface,
catalyst cannot catalyse a reaction of the poison,
becomes inactive because the active sites are blocked

Question 10

Regeneration of catalysts in cracking

Answer 10

soot blocks the adsorption of reactant molecules, catalyst is continuously recycled through a separate container where hot air is blown through the powder, the carbon is converted to CO2

Question 11

Zeolites

Answer 11

catalysts used in the cracking of long chain hydrocarbons