TITLE: How is it possible that combustion of coal releases similar energy as TNT explosion while intuitively we would not expect that?
QUESTION [16 upvotes]: According to Wikipedia, the energy released in a TNT explosion is 4 × 106 J/kg.
https://en.wikipedia.org/wiki/TNT
According to web, combusion of coal is around 24 × 106 J/kg.
https://www.world-nuclear.org/information-library/facts-and-figures/heat-values-of-various-fuels.aspx
This looks rather counter-intuitive: TNT is famous for the explosion, thus I would expect that it releases a lot of energy, but actually, it seems much smaller than coal combustion...
How is that possible that combustion of coal releases similar energy as a TNT explosion while intuitively we would not expect that?

REPLY [2 votes]: An explosion is, abstractly, the occurrence of a high rate of energy transformation in time: A lot of energy is "released" (that is, transformed from chemical or nuclear energy to radiation and heat) within a short interval. It is important enough that physics has a name for such a "energy density in time": Power.
Energy is more interesting when it is concentrated, also in space: A laser is more interesting than a diffuse light source, even though both may release the same amount of radiation over time. Here entropy comes into play: Concentrated energy is "usable" (the energy flow occurring when the entropy grows — i.e., when the concentrated energy disperses — can be put to use).
Because of limitations like the speed of the proliferation of nuclear and chemical reactions, and ultimately the speed of light, one requirement for a high-power explosion — a high concentration of energy in time — is a high concentration of energy in space beforehand.
{"set_name": "stack_exchange", "score": 16, "question_id": 576791}