Fuels

Recall what hydrocarbons are

Compounds that contain carbon and hydrogen only

Describe crude oil

A complex mixture of hydrocarbons. Contains molecules in which carbon atoms are in chains or rings. An important source of useful substances (fuels and feedstock for the petrochemical industry). A finite resource, hot, black, and sticky

Describe the separation of crude oil by fractional distillation

Crude oil is heated in the fractionating column. The oil evaporates and condenses at different temperatures (longer chains have higher boiling points). The column works continuously; heated crude oil is piped in at the bottom. Vaporised oil rises and fractions are tapped off at different levels where they condense

Recall the use of the fraction: Gases

Domestic heating and cooking

Recall the use of the fraction: Petrol

Fuel for cars

Recall the use of the fraction: Kerosene

Fuel for aircraft

Recall the use of the fraction: Diesel oil

Fuel for some cars and trains

Recall the use of the fraction: Fuel oil

Fuel for large ships and in some power stations

Recall the use of the fraction: Bitumen

Surface roads and roofs

Explain how fractions differ in number of atoms, boiling point, ignition, and viscosity

They differ in the number of C and H atoms. Shorter molecules: lower boiling point, easier to ignite, less viscous. Longer molecules: higher boiling point, harder to ignite, more viscous. Mostly members of the alkane homologous series

Explain a homologous series

A series of compounds which: have the same general formula; differ by CH₂; show gradual variation in physical properties (e.g., boiling points); have similar chemical properties

Describe the complete combustion of hydrocarbon fuels

A reaction in which: carbon dioxide and water are produced; energy is given out (exothermic)

Explain why incomplete combustion produces carbon and carbon monoxide

If there's not enough oxygen (partial combustion): solid particles of soot (carbon) and unburnt fuel are released. Carbon monoxide is produced when there isn't enough oxygen to form CO₂ instead

Explain how carbon monoxide behaves as a toxic gas

Colourless and odourless gas. If breathed in, it prevents red blood cells carrying oxygen around the body, which leads to death

Describe problems caused by incomplete combustion in appliances

Carbon monoxide causes health problems. Soot causes global dimming

Explain how sulfur dioxide is produced from fuels

Impurities (sulfur) in some hydrocarbon fuels react with oxygen when burnt to form sulfur dioxide

Explain problems associated with acid rain from sulfur dioxide

Damages buildings and statues (made of limestone). Reduces growth of or kills trees and crops. Lowers pH of water in lakes, killing fish

Explain how oxides of nitrogen are produced in engines

At high temperatures, oxygen and nitrogen from the air react to produce nitrogen monoxide. Released nitrogen monoxide combines with oxygen in air to form nitrogen dioxide. Both are pollutants

Advantage of hydrogen over petrol

Petrol is from crude oil, a finite resource. Hydrogen combustion only produces water (no CO₂ to contribute to global warming)

Disadvantage of hydrogen over petrol

Expensive. Difficult to transport and store. Dangerous - hydrogen can be explosive

Recall what petrol, kerosene and diesel oil are

Non-renewable fossil fuels obtained from crude oil

Recall what methane is

A non-renewable fossil fuel found in natural gas

Explain what cracking involves

Breaking down larger, saturated hydrocarbon molecules (alkanes) into smaller, more useful ones, some of which are unsaturated (alkenes)

Describe the process of cracking

Heat hydrocarbons to vaporise them. Vapours are either: passed over a hot catalyst, OR mixed with steam and heated to a very high temperature for thermal decomposition

Describe alkenes

Unsaturated hydrocarbons with the general formula CₙH₂ₙ. They have a double bond. First two are ethene and propene

Explain why cracking is necessary

Demand for smaller chained alkanes (e.g., petrol) is much greater than for longer chained alkanes. Shorter chained hydrocarbons ignite more easily and are more useful as fuels