During the combustion of coal, the carbon in the fuel combines with oxygen in the air to form carbon dioxide. In the cases where there is not enough oxygen for complete oxidation, carbon monoxide (CO) may form.
The hydrogen (H) in the coal oxidizes by combining with oxygen (O) and forms water (H2O).
The nitrogen in the coal turns into nitric oxide (NO) and nitrogen dioxide (NO2).
The sulfur turns into sulfur dioxide (SO2) and the inorganic minerals turn into ash particles.