How can we choose the best chemicals to create a cold or hot pack?

➷ It would depend on whether they would create an endothermic reaction or exothermic. For a hot pack, the chemicals would need to release energy (heat). However, a cold pack would need chemicals that need to draw heat from the surroundings to produce a cool sensation.

➶ Hope This Helps You!

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↬ ʜᴀɴɴᴀʜ ♡

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.