Exploding Oatcakes - more energy than TNT!!!!!!!

Hard to believe? The facts are easy to find. From published data, we can find that TNT yields about 4.25 megajoules of energy per kilogram when detonated, fairly typical for a high explosive.

Next, off to the kitchen cupboard. The oatcake packet tells me that oatcakes yield 18 megajoules per kilogram. This is more than 4 times as much energy as in the TNT.

So why are oatcakes so much less spectacular than TNT? It's because explosions are not so much about releasing a lot of energy, they're about releasing it very quickly. TNT certainly does that – an oatcake-sized amount of TNT releases its energy in a fraction of a microsecond. This creates huge gas pressures, and hence an explosion. An oatcake, on the other hand, takes minutes to burn.

Now there's one thing I haven't mentioned. Explosives include everything needed for the reactions that make them go bang, but an oatcake needs a source of oxygen. We really ought to include the mass of the oxygen along with the mass of the oatcake. The packet says that oatcakes contain a lot of carbohydrate, with about a third as much fat. Carbohydrate needs about its own mass of oxygen to burn, and fat needs about 3-4 times as much. It works out that a burning oatcake consumes about 1.5 times its own mass in oxygen. So the 18 megajoules that we get from a kilogram of oatcakes actually comes from about 2.5 kilograms of material. Even so, it still beats TNT.

There's another important factor: whereas the chemicals in explosives are already exactly in position and ready for action, the oxygen that an oatcake needs is not inside the oatcake. The rate at which the oatcake burns depends on how fast we can supply oxygen. If we could somehow incorporate enough oxygen right inside the oatcake, it might indeed go off with a bang. Would that make it a cracker?