Sorry for the delay BP.
Your example is one way. But being a reaction, it may take more energy to produce than you get back. Catalysts can help, if one exists for the particular reaction.
Fractionating Hydrocarbons simply takes heat. The steam process is a controled form of applying the Heat. As a Hydrocarbon chain is heated, it moves around violently and eventually breaks creating two shorter chains. More heat causes the shorter chains to break and so on, till eventually if you apply enough heat, the shortest chain divides. But interestingly, the long chains are the ones that need higher temperatures to break them, so in fact, as the chains break and become shorter, they do not require as much heat to continue the process as you would expect.
Yet another process is being discussed here