they burn in oxygen/air to form carbon dioxide and water.
incomplete combustion produces soot (carbon), carbon monoxide and water.
the reaction with ethane is very exothermic and the ease of burning depends on the size of the molecule.
substitution reactions with chlorine/bromine
alkanes are unreactive but they react slowly with halogens in the presence of UV/sunlight.
this type of reaction is free radical substitution where hydrogen in alkane is removed and substituted with a halogen.
alkanes slowly decolourise bromine water in the presence of sunlight. this can be used to identify alkanes.