# What exactly is Binding Energy and how is Energy released in a Nuclear Fusion?

Binding Energy of a nucleus can be found using the formula $$E = \Delta m\,c^2$$

Here, $$\Delta m$$ is the mass defect of the nucleus. Now, in a nuclear fusion reaction, we combine two lighter elements into a heavier element. But in this reaction, the total mass of initial two elements is greater than the heavier element. So some mass $$\Delta m$$ is converted to energy. But shouldn't this released energy ($$\Delta m\,c^2$$) go into forming the binding energy for the nucleus? But then why energy is still released into the surroundings?

• the mass of the combined nucleus is smaller than the combined masses of the original nuclei, and the “missing” mass is released as energy . Yes, and shouldn't this same "missing" mass convert into binding energy for holding the combined nuclei together? Aug 25, 2021 at 9:04
• @ Jdeep No. The mass defect is the binding energy. You don't have to add more energy when you fuse light nuclei - instead some of the binding energy present in the original nuclei is "repaid" and released into the environment. If you owe your brother two loans of \$25 each but he agrees to cancel the whole debt if you repay him \$30 then you are \\$20 better off than you were before. Aug 25, 2021 at 10:46