1. Chemical Reactions: These involve the breaking and forming of chemical bonds, releasing relatively small amounts of energy. Think of burning wood or a campfire.

2. Nuclear Fission: This process involves splitting a heavy atomic nucleus (like uranium) into lighter nuclei, releasing a significant amount of energy. This is the power source of nuclear power plants.

3. Nuclear Fusion: This process involves fusing two light atomic nuclei (like hydrogen) into a heavier nucleus, releasing an even greater amount of energy than fission. This is the power source of stars and the ultimate goal of fusion research.

In summary:

* Fusion >> Fission >> Chemical Reactions

Fusion releases the most energy, followed by fission, and then chemical reactions.