5.1 Combustion
- Fuel + oxygen = 1 or more combustion products/oxide
- (virtually) always exothermic
- Ful combustion: with plenty of oxygen
- Incomplete combustion: with a shortage of oxygen
( can create sooth and dirt)
- Slow combustion: without fire (or sparkles)
Incomplete combustion:
- At an incomplete combustion ( of a fuel of which the molecules do contain C-atoms), besides CO2 (g) also C (s) (=soot) is formed.
- Under certain circumstances also CO (g) (carbon mono-oxide) a very poisonous gas is formed.
Fighting fire:
- Fighting fires can be done by multiple ways. The first option is water. The water lowers the temperature and because the water
evaporates, it expels the oxygen. However, when fat is on water it is dangerous to try water (it can cause an explosion)
- It is also possible to fight fire by taking away the combustible substance.
Combustion of elements:
- For a combustion reaction, oxygen is always needed. When a combustible substance consist of just one element, an oxide will
always be formed. An oxide is a compound made up of two kinds of atoms; the element oxygen and the element which was
combusted.
- When you combust a metal, an metal oxide is formed. In the name of the metal oxide you write the name of the metal followed
by the word oxide. Some metals can form more than one oxide and this is indicated by a Roman numeral in the name.
- When you combust a non-metal it can also result in more than one oxide. In naming them, numeric prefixes are used to indicate
the ratio between the element and oxygen. Therefore: 1, Mono & 2, Di & 3, Tri & 4, Tetra & 5, Penta
Combustion of compounds:
- The molecules of a compound consist of different kinds of atoms. When combusting a compound, each kind of atom will form
its own oxide. The reaction products of a combustion depend on the kinds of atoms in the combustible substance. (more info in
incomplete combustion)
Reaction products of a combustion (example):
Element in the compound Complete combustion Incomplete combustion
C CO2 CO, C
H H2O H2O
S SO2 SO2
Reagents:
- A reagent is a substance that will change visibly in contact with the substance you want to identify.
Reagent Substance to be identified Observation
White copper sulphate Water / water vapour White copper sulphate turn blue
Clear lime water Carbon dioxide Clear lime water turns turbid
Bromine water Sulfur dioxide Brown bromine water turns
colourless
Explosive combustion reactions
- In an explosion many forces are released and these can cause many buildings to be destroyed. Not all substances are suitable
for causing an explosive combustion reaction. Here fore there must be two additional conditions:
- The combustible substance and oxygen need to be mixed in the correct ratio
- There must be an exothermic reaction, in which gaseous reaction products are formed
- As a result of heat the gasses will expand fast and strong. This is called an explosion.
- Fuel + oxygen = 1 or more combustion products/oxide
- (virtually) always exothermic
- Ful combustion: with plenty of oxygen
- Incomplete combustion: with a shortage of oxygen
( can create sooth and dirt)
- Slow combustion: without fire (or sparkles)
Incomplete combustion:
- At an incomplete combustion ( of a fuel of which the molecules do contain C-atoms), besides CO2 (g) also C (s) (=soot) is formed.
- Under certain circumstances also CO (g) (carbon mono-oxide) a very poisonous gas is formed.
Fighting fire:
- Fighting fires can be done by multiple ways. The first option is water. The water lowers the temperature and because the water
evaporates, it expels the oxygen. However, when fat is on water it is dangerous to try water (it can cause an explosion)
- It is also possible to fight fire by taking away the combustible substance.
Combustion of elements:
- For a combustion reaction, oxygen is always needed. When a combustible substance consist of just one element, an oxide will
always be formed. An oxide is a compound made up of two kinds of atoms; the element oxygen and the element which was
combusted.
- When you combust a metal, an metal oxide is formed. In the name of the metal oxide you write the name of the metal followed
by the word oxide. Some metals can form more than one oxide and this is indicated by a Roman numeral in the name.
- When you combust a non-metal it can also result in more than one oxide. In naming them, numeric prefixes are used to indicate
the ratio between the element and oxygen. Therefore: 1, Mono & 2, Di & 3, Tri & 4, Tetra & 5, Penta
Combustion of compounds:
- The molecules of a compound consist of different kinds of atoms. When combusting a compound, each kind of atom will form
its own oxide. The reaction products of a combustion depend on the kinds of atoms in the combustible substance. (more info in
incomplete combustion)
Reaction products of a combustion (example):
Element in the compound Complete combustion Incomplete combustion
C CO2 CO, C
H H2O H2O
S SO2 SO2
Reagents:
- A reagent is a substance that will change visibly in contact with the substance you want to identify.
Reagent Substance to be identified Observation
White copper sulphate Water / water vapour White copper sulphate turn blue
Clear lime water Carbon dioxide Clear lime water turns turbid
Bromine water Sulfur dioxide Brown bromine water turns
colourless
Explosive combustion reactions
- In an explosion many forces are released and these can cause many buildings to be destroyed. Not all substances are suitable
for causing an explosive combustion reaction. Here fore there must be two additional conditions:
- The combustible substance and oxygen need to be mixed in the correct ratio
- There must be an exothermic reaction, in which gaseous reaction products are formed
- As a result of heat the gasses will expand fast and strong. This is called an explosion.
