Doesn’t fusion release energy, while fission requires it?
In: Chemistry
Short answer: no, both fusion and fission can be exothermic.
Long answer: whether a reaction is exothermic or endothermic depends on the deltaH value. Regardless of whether a reaction is fusion or fission, if the deltaH value for the reaction is negative, you have an exothermic reaction; if the deltaH value is positive, you have an endothermic reaction.
https://opentextbc.ca/introductorychemistry/wp-content/uploads/sites/17/2014/06/signs_of_enthalpy_and_entropy_terms_and_spontaneity.png
That chart explains the values of the Gibbs free energy equation in relation to spontaneity (rightmost column.) In order for a reaction to naturally occur, it needs to be spontaneous so the bottom three possibilities are what we are looking for – as you can see, while it is easier for exothermic reactions to happen when deltaH is negative (generally associated with breaking bonds) it is also possible when deltaH is positive (generally associated with making bonds.)
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