chap 18 fuels and crude oil

Question 1

what are fuels

Answer 1

substances that can be burnt in air to give out energy that can be used to power motor vehicles and generate electricity

Question 2

how are fossil fuels formed

Answer 2

formed from remains of living things and animals that are covered under the seabed over millions of years

Question 3

what does complete combustion of hydrocarbons in oxygen produce

Answer 3

carbon dioxide, water and energy (exothermic)

Question 4

when does incomplete combustion of hydrocarbons occur

Answer 4

when insufficient oxygen is present

Question 5

what does incomplete combustion of hydrocarbons produce

Answer 5

soot and carbon monoxide

Question 6

what are the two types of fossil fuels

Answer 6

natural gas and crude oil

Question 7

characteristics and constituents of natural gas

Answer 7

colourless, odourless gas. mainly methane

Question 8

characteristics and constituents of crude oil

Answer 8

dark and sticky liquid. mixture of different hydrocarbons (mainly alkanes)

Question 9

why is natural gas considered the “cleanest” fossil fuel

Answer 9

it has the lowest percentage of carbon by mass

Question 10

how can crude oil be separated

Answer 10

via fractional distillation based on their boiling points

Question 11

hydrocarbons with larger molecules (more carbon) ->

Answer 11

higher boiling points

Question 12

hydrogen with smaller molecules (less carbon) ->

Answer 12

lower boiling points

Question 13

why are natural gases and crude oil a non renewable source of energy

Answer 13

there are limited amounts of these sources and they cannot be replaced quickly enough to keep up with our rate of use

Question 14

how does a fractional distillation work to separate crude oil (5)

Answer 14

• crude oil is heated in a furnace and vapour is passed into the fractionating column
• fractionating column is hottest at the bottom and gets cooler towards the top
• the different fractions condense at different levels are collected at the respective outlets
• the fractions with higher boiling points condense at higher temperatures and are collected at the lower levels of the fractionating column
• the fractions with lower boiling points rise further up the column before they condense and are collected

Question 15

why do hydrocarbons with smaller molecules have lower boiling points

Answer 15

smaller molecules have weaker intermolecular forces of attraction which requires smaller amounts of energy to overcome

Question 16

why are hydrocarbons with smaller molecules less viscous

Answer 16

weaker intermolecular forces of attraction allows the molecules to slide over one another easier

Question 17

what are the issues of using crude oil fractions

Answer 17

supply of crude oil is limited

Question 18

ways to conserve crude oil (3)

Answer 18

• reduce usage (take public transport)
• use alternative energy sources (solar energy, nuclear energy, renewable energy)
• improve design of power stations and vehicles (research, innovation and technology)

Question 19

what are biofuels

Answer 19

alternative renewable energy sources to crude oil and natural gases

Question 20

source of biofuels

Answer 20

plants and animals