Carbon: reactions of elements
Reaction of carbon with air
Carbon, as graphite, burns to form gaseous carbon (IV) oxide (carbon dioxide), CO2. Diamond is a form of carbon and also burns in air when heated to 600-800°C - an expensive way to make carbon dioxide!
C(s) + O2(g) → CO2(g)
When the air or oxygen supply is restricted, incomplete combustion to carbon monoxide, CO, occurs.
2C(s) + O2(g) → 2CO(g)
This reaction is important. In industry, air is blown through hot coke. The resulting gas is called producer gas and is a mixture of carbon monoxide (25%), carbon dioxide (4%), nitrogen (70%), and traces of hydrogen (H2), methane (CH4), and oxygen (O2).
Reaction of carbon with water
Carbon, either as graphite or diamond does not react with water under normal conditions. Under more forsing conditions, the reaction becomes important. In industry, water is blown through hot coke. The resulting gas is called water gas and is a mixture of hydrogen (H2, 50%), carbon monoxide (CO, 40%), carbon dioxide (CO2, 5%), nitrogen and methane (N2 + CH4, 5%). It is an important feedstock gas for the chemical industry.
C + H2O → CO + H2
This reaction is endothermic (ΔH° = +131.3 kJ mol-1; ΔS° = +133.7 J K-1 mol-1) which means that the coke cools down during the reaction. To counteract this, the steam flow is replaced by air to reheat the coke allowing further reaction.
Reaction of carbon with the halogens
Graphite reacts with fluorine, F2, at high temperatures to make a mixture of carbon tetrafluoride, CF4, together with some C2F6 and C5F12.
C(s) + excess F2(g) → CF4(g) + C2F6 + C5F12
At room temperatur, the reaction with fluorine is complex. The result is "graphite fluoride", a non-stoichiometric species with formula CFx (0.68 < x < 1). This species is black when x is low, silvery at x = 0.9, and colourless when x is about 1.
The other halogens appear to not react with graphite.
Reaction of carbon with acids
Graphite reacts with the oxidizing acid hot concentrated nitric acid to form mellitic acid, C6(CO2H)6.