The quality or degree to which a reaction or process is exothermic; the amount of heat released.
From exothermic + the suffix -ity meaning 'quality' or 'state.' This noun abstracts the concept of heat-release into a measurable property.
Different reactions have different exothermicities—fireworks are wildly exothermic while dissolving sugar in water is only slightly exothermic, and measuring these differences tells us how much energy we can get from different processes!
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