Introduction part 2: combustion, substitution and addition

All organic compounds at IGCSE undergo combustion reactions

What is combustion?'

Chemical reaction in which a substance reacts with oxygen (burns) to form products and heat

What products are formed during the combustion of hydrocarbons in:

• Excess oxygen

• Limited supply of oxygen

• Excess: complete combustion produces CO₂ and H₂O + large amount of heat energy

• Limited: incomplete combustion produces CO or carbon (soot) and H₂O + large amount of heat energy

Explain why incomplete combustion of hydrocarbons might be dangerous for humans

Carbon monoxide is a colourless, odourless and very poisonous gas

• It is poisonous because it reduces the ability of the blood to carry oxygen around the body

• This will make you ill or you may even die, because not enough oxygen gets to the cells in your body for respiration to provide energy

What is propane frequently used for when burned?

Used in camping stoves outdoors

What is a substitution reaction?

A chemical reaction in which an atom or group of atoms in a molecule is replaced by a different atom or group of atoms

Give an example of a substitution reaction + give the equation (displayed or structural)

Methane reacts with bromine under ultraviolet light

What is an addition reaction?

A chemical reaction in which one molecule adds to another without taking anything away, to form a single larger molecule (no other products are formed)

• Only alkenes undergo addition reactions

Give an example of an addition reaction + the equation (displayed or structural)

For example, ethene reacts with bromine to produce 1,2-dibromoethane