Why did the Comet Shoemaker-Levy-9 fragments cause such large explosions on Jupiter? In July 1994, the comet Shoemaker-Levy 9 (D/1993 F2) tidally fragmented and these fragments collided into Jupiter, as per the image below.



Image source

The question is, what mechanisms resulted in these small fragments causing such large explosions in the Jovian clouds?
Shoemaker Levy 9 was estimated to have released kinetic energy equivalent to 300 gigatons of TNT. That is $1.255 \times 10^{21} {\rm J}$. This release through friction and compression was sufficient to heat the atmosphere to 4000K at first. That in turn should probably be enough to break down the molecular hydrogen and methane, releasing further energy. But that's only my guess. The heating from the impact alone should make a huge fireball.
Sources:
Fragment Size and Mass Estimates
Galileo observations