Both fusion and fission are nuclear reactions. why is a very high temperature required for fusion, but not for fission?

Explanation:

A nuclear fusion is defined as the reaction in which two small nuclei will combine together and result in the formation of a heavier nuclei.

As the nucleus of both the combining atoms are involved in a nuclear reactions. Hence, there will be electron clouds repulsion between these combining nuclei.

Therefore, these atoms will not be able to combine then. As a result, very high heat or temperature must be provided so that these electronic repulsion can overcome and tend to form a heavier nuclei.

your parents i think this could be it

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"