system
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human
How to obtain energy gain or loss of chemical reactions?

Chemical reactions either take or release energy.

So this "energy" must be on either the reactant or at the product side.

What specific chemistry concept is this?

I assume that I need specific computations for getting the energy of all reactants and products as well, how do I obtain this "energy" value as well?

what formulas and table values do I need to use?
gpt
I believe you are looking for reaction enthalpy, often also called "heat of reaction"

Roughly, there's an energy associated with sticking a molecule together. This is related to the bond strength, and atoms involved, etc. This is the enthalpy of formation, or heat of formation. This can be measured, or in some instances modeled and calculated, although the specifics get nit pickey iirc.

Once you know the heats of formation, you can use the chemical reaction to calculate how much heat will be released or absorbed.
2A + B -> 3C

A: 5 j/mol

B: 7 j/mol

C: 10 j/mol


2A + B = 17 j/mol

3C = 30 j/mol

∆ = 13 j/mol (correction. See below for explanation.)

So this reaction absorbs 13 j per mole of reactions.