fractional distillation
What is crude oil?
A mixture of hydrocarbons
What is the general formula for alkanes?
CₙH₂ₙ₊₂
Are alkanes soluble in water?
no
What is cracking?
Breaking down long-chain hydrocarbons into shorter ones
What is formed in complete combustion?
carbon dioxide and water
What property is used to separate hydrocarbons in fractional distillation?
boiling point
What type of bonds are found in alkanes?
Single covalent bonds
What happens to boiling point as chain length increases?
it increases
Name one useful product of cracking
alkenes or petrol
What is incomplete combustion?
Burning with limited oxygen
Where are the shortest-chain hydrocarbons collected in the column?
at the top
Are alkanes saturated or unsaturated?
saturated
Which is more viscous: short or long-chain alkanes?
long chain alkanes
What conditions are needed for thermal cracking?
high temperature or pressure
Name one product of incomplete combustion
carbon monoxide or soot
Why do longer-chain hydrocarbons have higher boiling points?
stronger intermolecular forces
Name C₅H₁₂
pentane
Why are short-chain alkanes more flammable?
They vaporise easily and mix with oxygen
What is used in catalytic cracking?
A catalyst and lower temperature
Write the word equation for methane combustion
Methane + oxygen → carbon dioxide + water
Explain why hydrocarbons condense at different heights
Each has a different boiling point, so they condense where the temperature matches their boiling point
Why are alkanes relatively unreactive?
Strong C–C and C–H bonds / no double bonds
Explain the trend in intermolecular forces across alkanes
More electrons → stronger intermolecular forces → higher boiling points
Why is cracking important for industry?
Produces fuels in demand + alkenes for plastics
Balance this symbol equation:
CH₄ + O₂ → CO₂ + H₂O
CH₄ + 2O₂ → CO₂ + 2H₂O