How is energy involved in determining if a reaction is classified as endothermic or exothermic

Chemical reactions love stability.
Usually if heat is given off, the chemicals are happier as they are more stable.
This should happen naturally, like a ball rolling down a hill.
But if you force chemicals to do things that make them more unstable, you're going to have to put energy in.
Like forcing a ball up a hill, it isn't naturally going to roll up without you putting in energy.
"exo-" means "away from" and "endo-" means "within". Think about this in terms of heat, or energy.
heat released -> exothermic reaction (energy escapes)
heat put in -> endothermic reaction (energy is put within)

Also the word "enthalpy" and ΔH is used a lot to relate to energy.

A negative ΔH means heat loss and a positive ΔH means heat put in as well.

Hope this helps ;)

Officialalehpeter Officialalehpeter · Answer 2 · 2020-02-03T12:10:42+01:00

Answer:

An endothermic reaction is one that absorbs energy in the form of heat or light. An exothermic reaction is a chemical reaction that releases energy through light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation: reactants → products + energy.

When energy is released as heat, the process is exothermic, and when heat is absorbed, the process is endothermic. An endothermic reaction is one which results in a net decrease in temperature because it absorbs heat from the surroundings and stores the energy in the bonds formed in the reaction.

So if the sum of the enthalpies of the reactants is greater than the products, the reaction will be exothermic. If the products side has a larger enthalpy, the reaction is endothermic.

Explanation: