[cbloom]

The total calories burned from two short sessions is most likely slightly greater than calories burned from one longer session (because you're fresher and running harder, and because you're elevating your heart rate for a while after twice instead of once). You will be burning primarily just short term free energy in a short session like that, you burn more fat in a longer session, but that's actually a misleading fact because all that matters in the end is your total calorie delta.

A 30 minute jog isn't really gonna do a lot for you though. It would be way better to do sprints or hill-runs or stairs or something more intense. Even better would be one session of sprints and another session of something more like weights. Even if you can't get to the gym you can find a bar and do pushups, pullups, etc...