Alkanes

Question 1

what is the general formula for an alkane

Answer 1

CnH₂n+₂

Question 2

what are the 3 reactions alkanes undergo

Answer 2

• combustion reactions
• cracking
• substitution with halogens

Question 3

describe cracking

Answer 3

• cracking is the breaking molecules into smaller ones
• the cracking of decane produces ethene, propene and pentane
• 540℃ required

Question 4

describe complete combustion of methane

Answer 4

• alkanes burn well in a good supply of oxygen to form carbon dioxide, water vapour and heat energy
• CH₄+ 2O₂ → CO₂ + 2H₂O + heat energy

Question 5

describe incomplete combustion of methane

Answer 5

• when there’s insufficient oxygen supply alkanes undergo incomplete combustion to form carbon monoxide
• CH₄ + 3O₂ → 2CO + 4H₂O + heat energy

Question 6

describe a substitution reaction with methane

Answer 6

-alkanes react with halogens (chlorine/bromine) in the presence of UV light
CH₄ + Cl₂ → CH₃Cl + HCl

methane + chlorine → chloromethane + hydrogen bromide

Question 7

properties of alkanes

Answer 7

• they are saturated
• they are non-polar
• they have carbon-carbon single bonds
• boiling points increase with chain length because attraction between molecules increases
• generally unreactive
• found in petroleum and natural gas
• simplest family of organic compounds