Battle of the Exothermic Redox Reactions

We've covered both thermite and "rocket candy." Here is a video of each, with 5g of thermite and 6g of rocket candy.

Here is the thermite (iron oxide with aluminum for fuel).

And here is the rocket candy (potassium nitrate with sugar for fuel):

A few things jump out at you:

1) The thermite is very hard to ignite (24s), but the sugar candy is pretty easy to ignite (<1s).

2) The thermite releases more energy in general.

3) The thermite releases more energy in the form of light.

4) The sugar candy has a longer burn (4s). The thermite is done in 2s.

5) The sugar candy releases many more gasses. 

6) If you can see in the videos, the thermite melts its aluminum cup and the sugar candy does not.

It goes without saying that sugar candy is a better propellant. Thermite actually is not a propellant at all; solids react to create solid products. Sugar candy has a longer burn with more emissions. This is what you want for thrust. Additionally, the thermite is just too hard to ignite and burns too hot to propel an actual vehicle.

That being said, the thermite can be used for welding because it leaves molten iron as a product. Since it carries all of its own oxygen in the iron oxide, burns so hot, and has no gas propellants, it can even be used underwater.

The application of chemistry is using the right tool for the job. Changing an atom here or there creates very different chemical properties and reactivity. 

Thanks for reading,

Paul