Let’s face facts: alkanes don’t have many uses. In real life, they are non-polar solvents, larger-chain ones can be used to make wax, and they are good for burning/they make good fuels. As far as organic chemistry goes, alkanes are very boring. They have only three uses in your class:
1) Solvents: Alkanes are very good non-polar solvents.
2) Halogenation: Alkanes can be reacted with bromine or chlorine under free-radical conditions to obtain an alkyl halide.
3) Combustion: This is the fuel part. Complete combustion is an alkane reaction with oxygen to obtain CO2 and water, as shown in the following example: C3H8 +5O2 –> 3CO2 + 4H2O + Heat
There is only a small possibility that you will see a combustion reaction on one of your exams. Therefore, the only real uses for alkanes in your undergraduate organic chemistry class will be as a solvent or in a halogenation reaction. Hence, if you have an alkane in one of your exam reactions, it should be very simple to determine its role. If there is a halogen (usually either Br2 or Cl2) , then beware of a halogenation reaction. Otherwise, it is most likely safe to say that if you have an alkane in your reaction, it is a solvent and does not participate as a reactant.