crude oils and fuels

Question 1

what is a hydrocarbon?

Answer 1

a compound formed from carbon and hydrogen atoms only.

Question 2

what is an alkane?

Answer 2

the simplest type of hydrocarbon. CₙH₂ₙ₊₂
saturated compounds. each carbon atom forms 4 single covalent bonds

Question 3

what are the first 4 alkanes? and their formulas

Answer 3

1. methane. CH₄
2. ethane. C₂H₆
3. propane. C₃H₈
4. butane. C₄H₁₀

Question 4

how do the properties of a hydrocarbon change as the length of the carbon chain increases?

Answer 4

1. a long chain is less runny than a short one.
2. a long chain is less volatile than a short one. higher boiling point etc
3. a long chain is less flammable than a short one.

Question 5

what is the formula for the complete combustion of a hydrocarbon?

Answer 5

hydrocarbon + oxygen → carbon dioxide + water + energy

Question 6

how is crude oil formed?

Answer 6

the remains of plants and animals that were buried in mud.
over millions of years high temperature and pressure remains turn to crude oil.

Question 7

why are fossil fuels called non renewable fuels?

Answer 7

they take so long to form so they are being used up quicker than they can regenerate. one day they will run out

Question 8

how can fractional distillation be used to separate hydrocarbons from crude oil?

Answer 8

crude oil is a mixture of different hydrocarbons.
1. crude oil is heated until most of it has turned to gas which enters a fractionating column.
2. in the column there is a temperature gradient. it’s hot at the bottom and cooler as it goes up
3. longer hydrocarbons have high boiling points and so condense near the bottom and drain out.
4. shorter hydrocarbons have low boiling points and so condense near the top and drain out.
5. you end up with a crude oil mixture separated into different fractions.

Question 9

what is crude oil used for?

Answer 9

fuel for transport.
petrochemical industry. polymers lubricants solvents detergents

Question 10

what is cracking?

Answer 10

splitting long hydrocarbons into short ones.

Question 11

what do you get from cracking other than alkanes?

Answer 11

alkanes.
alkenes. a starting material for other compounds

Question 12

how do you do cracking?

Answer 12

1. cracking is a thermal decomposition reaction. breaking molecules by heating them
2. heat long hydrocarbons to turn them to gas.
3. the vapour is passed over a hot powdered aluminium oxide catalyst.
4. long chain molecules split apart on the surface of the catalyst. catalytic cracking
   or
5. turn long hydrocarbons to gas.
6. mix them with steam and heat them very high. steam cracking

Question 13

what is an alkene?

Answer 13

unsaturated hydrocarbon compounds. because they have a double carbon bond