Topic 8 – Fuels + Earth and atmospheric science

Hydrocarbons definition |

Compounds containing carbon and hydrogen only.

Crude oil is… |

A complex mixture of hydrocarbons.

Crude oil molecules can be…

Carbon atoms in chains or rings (no specific ring names needed).

Why is crude oil important?

Source of fuels and feedstock for the petrochemical industry.

Crude oil is a finite resource because… |

It will run out (non-renewable).

How is crude oil separated? |

Fractional distillation.

Fractional distillation (what happens?) |

Crude oil is heated so it vaporises; vapours condense at different heights due to different boiling points.

Why do fractions separate in a column? |

Different fractions have different boiling points.

Fractions: gases use |

Domestic heating and cooking.

Fractions: petrol use |

Fuel for cars.

Fractions: kerosene use |

Fuel for aircraft.

Fractions: diesel oil use

Fuel for some cars and trains.

Fractions: fuel oil use |

Fuel for large ships and some power stations.

Fractions: bitumen use |

Surfacing roads and roofs.

How do fractions differ in molecule size? |

Different numbers of carbon and hydrogen atoms (chain length).

How does chain length affect boiling point? |

Longer chains → higher boiling point.

How does chain length affect ease of ignition? |

Shorter chains ignite more easily.

How does chain length affect viscosity? |

Longer chains are more viscous (thicker).

Most hydrocarbons in fractions are… |

Alkanes (homologous series).

Homologous series definition |

Same general formula, differ by CH₂, gradual change in physical properties (e.g. boiling point), similar chemical properties.

homoglous formula?

CnH2n+2

Complete combustion of hydrocarbons produces

Carbon dioxide and water.

Complete combustion gives out…

Energy (exothermic).

Why does incomplete combustion happen?

Not enough oxygen.

Incomplete combustion can produce?

Carbon (soot) and carbon monoxide.

Why is carbon monoxide toxic?

It binds to haemoglobin and reduces oxygen transport in blood.

Problems caused by CO and soot

CO can kill; soot causes respiratory problems and dirty appliances.

Why does sulfur dioxide form when fuels burn? |

Impurities containing sulfur in the fuel burn to form SO₂.

Problems caused by acid rain (SO₂ dissolving in rain) |

Damages plants and aquatic life; erodes limestone buildings; corrodes metals.

Why do engines produce oxides of nitrogen (NOx)? |

At high temperatures nitrogen and oxygen in air react.

Hydrogen vs petrol as car fuel (advantages of hydrogen) |

Produces only water, less pollution/CO₂.

Hydrogen vs petrol as car fuel (disadvantages of hydrogen) |

Storage/transport difficult, expensive infrastructure, hydrogen production may use fossil fuels.

Which fuels are non-renewable fossil fuels from crude oil? |

Petrol, kerosene, diesel oil.

Methane is… |

A non-renewable fossil fuel found in natural gas.

Explain why incomplete combustion of hydrocarbons can produce carbon and carbon monoxide

Incomplete combustion happens when there is not enough oxygen. The carbon in the hydrocarbon is not fully oxidised to CO₂, so it forms carbon monoxide (CO) or solid carbon (soot) instead.

Explain cracking

Cracking is when large saturated hydrocarbons (alkanes) are broken down into smaller, more useful hydrocarbons, producing a mixture of shorter alkanes and unsaturated alkenes (because some molecules lose hydrogen and form a C=C double bond).

What is cracking? |

Breaking large saturated hydrocarbons (alkanes) into smaller, more useful molecules, some unsaturated (alkenes).

Why is cracking necessary?

To produce more short-chain fuels (high demand) and to make alkenes for polymers/chemicals.

What formed Earth’s early atmosphere? |

Gases produced by volcanic activity.

Early atmosphere contained and evidence|

Little/no oxygen, lots of carbon dioxide, water vapour, small amounts of other gases. Evidence comes from volcanic gases today and rocks/atmospheric records showing very low oxygen early on and high carbon dioxide levels.

How did water vapour form oceans? |

condensed as Earth cooled.

Why did atmospheric CO₂ decrease as oceans formed? |

CO₂ dissolved in the oceans.

How did oxygen increase in the atmosphere? |

Primitive plants photosynthesised: used CO₂ and released O₂, so O₂ gradually increased.

Chemical test for oxygen |

Relights a glowing splint.

Greenhouse effect definition |

Gases like CO₂, methane and water vapour absorb heat radiated from Earth and re-release it, keeping Earth warm.

Evidence for human activity causing climate change |

Correlation between rising CO₂, fossil fuel use, and temperature increase.

Uncertainties in climate data |

Measurements depend on location and historical accuracy.

Composition of today’s atmosphere |

About 78% nitrogen, 21% oxygen, small amounts of argon, carbon dioxide and water vapour.

Effects of increased CO₂ and methane |

Enhanced greenhouse effect → global warming/climate change.

Human activities increasing CO₂ and methane |

Burning fossil fuels (CO₂) and livestock farming (methane).

How can climate change effects be mitigated? |

Reduce emissions, use renewables, carbon capture, improve efficiency (consider scale, risk, environmental impact).