Burning + Cracking Hydrocarbons

Question 1

complete combustion

Answer 1

burnt in plenty of air - hydrocarbon fully oxidised, produces carbon dioxide and water, energy transferred to surroundings

Question 2

how do you test for complete combustion?

Answer 2

lime water, showing carbon dioxide is present

Question 3

incomplete combustion

Answer 3

not burnt in enough air, engine, producing carbon monoxide

Question 4

why do we crack long chain hydrocarbons?

Answer 4

low demand, not useful as poor fuels

Question 5

cracking

Answer 5

breaking down of long, less useful hydrocarbon molecules into short, more useful hydrocarbon molecules, thermal decomposition reactions occur

Question 6

cracking process

Answer 6

oil refinery = cracker, heavy fractions (distilled from crude oil) heated to vaporise hydrocarbons, vapour is passed dover high temperature catalyst or mixed with steam and heated at high temperatures

Question 7

alkene

Answer 7

unsaturated molecules, containing at least one double bond of carbon atoms via covalent bonding, 2 less hydrogen atoms than alkanes

Question 8

reaction for alkanes

Answer 8

bromine water, orange to colourless

Question 9

why are alkenes more reactive than alkanes?

Answer 9

double carbon bonding

Question 10

homologous series

Answer 10

of same functional group e.g. C=C

Question 11

why do alkenes release less energy and produce a more yellow, smoky flame than alkanes when burnt?

Answer 11

incomplete combustion

Question 12

alkene reacting with hydrogen

Answer 12

addition of hydrogen molecule across C=C, turning into alkane and straightens molecules + increases melting point

Question 13

alkene reacting with steam

Answer 13

ethene reacts with steam to produce ethanol