Solution: From a molecular viewpoint, where does the energy emitted in an exothermic chemical reaction come from?

Problem

From a molecular viewpoint, where does the energy emitted in an exothermic chemical reaction come from?

Solution

We’re being asked to explain where the energy emitted in an exothermic reaction comes from.


Recall that:

Exothermic reactions

lose energy, releases heat, temperature of the surroundings increases
▪ involves bond formation (for phase change: gas → liquid → solid)
ΔH is negative

Endothermic reactions

gain/requires energy, absorbs heat, temperature of the surroundings decreases
▪ involves breaking bonds (for phase change: solid → liquid → gas)
ΔH is positive

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