How are chemical reactions involved in the transformation of matter?

I occasionally develop an interest in nuclear power plants, accidents, atom bombs, and related topics.

One example of "chemical reactions involved in transformation of matter" is the large explosion that blew the top off the reactor building of two or three buildings at Fukushima after the earthquake (the word "meltdown" is in parenthesis because in one case, the problem was the spent fuel pool, not necessarily the reactor, but in another case, it was a reactor).

This hydrogen gas built up in the upper levels of the structure until it finally exploded, converting the hydrogen gas back into water.

It's similar to a rollercoaster ride on stability; given enough energy and a reactive substance like zircaloy decomposition, you can chemically convert water into hydrogen gas and oxygen, two very different substances. The hydrogen gas is suddenly much more unstable and has a higher energy, and when it comes into contact with an ignition source, it slides down the thermodynamic hill to reform stable water while also expending a lot of the energy it had gained (by blowing off the top of the building).

I know it's a huge oversimplification, but sometimes my mind functions like a Far Side comic strip.

Chemical reactions involve the breaking and forming of chemical bonds between atoms. This process changes the arrangement of atoms and results in the transformation of substances into different substances with different properties.