Why is fusion exothermic?
Fusion is exothermic because the mass of the products is lower than the mass of the two reacting nuclei.
Here are some typical masses:
- neutron = 1.009 u
- deuterium nucleus = 2.014 u.
- tritium nucleus = 3.016 u
- helium nucleus = 4.003 u
In a fusion reaction, two light nuclei fuse together and form a heavier nucleus.
The mass of the products is less than the mass of the two reacting nuclei.
For example, deuterium and tritium nuclei fuse to form a helium nucleus (α particle) and a neutron.
The difference in masses is
The product nuclei have less mass than the reactants.
This difference in mass is given off in the form of energy (
A fusion reaction is exothermic.