What is the difference between an exothermic process and an exothermic reaction?

Jul 8, 2017

Well, basically, one is more general than the other. But there aren't that many differences.

Some similarities and differences (in the context of aqueous solutions):

$\underline{\text{Exothermic"" "" ""Exothermic Reaction}}$

$\text{General"" "" "" "" ""Only for reactions}$

$\text{Releases heat?"" "" ""Releases heat}$

DeltaH < 0?" "" "" "" "DeltaH_(rxn) < 0

DeltaT_(sys) < 0?" "" "" "DeltaT_(sol n) > 0

The reason why there are ?'s is that for a general thermodynamic process, we must specify the reference point.

A process can be exothermic or endothermic with respect to the system, or the surroundings, and it's our choice! It's our choice what the system/surroundings are, and what perspective we want to speak from.

As an example, if a process is endothermic with respect to the aqueous solution, then $\Delta {T}_{s o l n} > 0$ (the solution gets hotter), and it could be due to $\left(1\right)$ an exothermic reaction, or it could be $\left(2\right)$ a liquid vaporizing.

These scenarios are typically considered with the following conventions:

Case $\left(1\right)$: Exothermic reaction in solution

If the reaction is not super hot, and the solution can "take the heat", so to speak,

System: reaction (from its perspective, exothermic)
Surroundings: solution (from its perspective, endothermic)

OR, if the reaction is hot enough, and the solution releases heat,

System: solution (from its perspective, exothermic)
Surroundings: the atmosphere (from its perspective, endothermic)

Case $\left(2\right)$: A liquid vaporizing

System: solution (from its perspective, exothermic)
Surroundings: the atmosphere (from its perspective, endothermic)

And as you can see, we arbitrarily made the solution the surroundings in one context and the system in the other context, depending on what makes the most sense to focus on.

It's very important you keep your system and surroundings straight, and figure out what someone else's choices are implied to be.