How do both fusion and fission bombs create an exothermic reaction?

Question

Doesn’t fusion release energy, while fission requires it?

In: Chemistry

Answer 1

Adding oxygen to hydrogen to make water is exothermic. Adding oxygen to water to make peroxide is endothermic. How can adding oxygen be both?

With nuclear reactions, like chemical ones, whether energy is absorbed or released depends on the components of the reaction. Typically, small nuclei release energy when fusing, large ones release energy while fissioning (fizzing?). Fission bombs use uranium and plutonium, very large nuclei, while fusion bombs use hydrogen, the smallest one.