# What are good representatives for the concepts of endergonic and exergonic?

We must demonstrate two reactions: endergonic and exergonic. I'm wondering if thefollowing reactions are accurate.

• Exergonic: I have sodium bicarbonate and vinegar. Would it be catabolic, spontaneous, and $-\Delta G$ as well?

Sodium bicarbonate and vinegar is your basic science-fair volcano reaction. You have the baking soda in a container of some sort and pour the vinegar. The formula would be something like $$\ce{Bicarbonate of soda + vinegar -> Carbonic acid + Water + Carbon dioxide gas}.$$

• Endergonic: I have ammonium chloride and water. Would it be anabolic, nonspontaneous, and $+\Delta G$?

Ammonium chloride would be dissolved into the water. The formula would be something like $$\ce{NH4Cl + water -> NH4+ + Cl-}$$

I've just barely touched on the $G$ value thing. I don't exactly know what's going on there. What I mean I guess is that if it's $+\Delta G$, the enthalpy increases, and if it's $-\Delta G$, the enthalpy decreases. To be more precise, we're on the Gibbs free energy lesson at the moment.

Endergonic means energy is absorbed during the reaction. Exergonic means that energy is released during the reaction. Is energy released or absorbed during a vinegar and baking soda reaction? Is energy released or absorbed when dissolving ammonium chloride and water?

• I think you should describe the processes better. Do you mean disolution of salts or what? When you give G values, always specify the process, i.e, the initial state and final state. – user43021 Oct 4 '17 at 15:28
• @HernanMiraola I edited my post a bit. Thank you – Amanda Oct 4 '17 at 15:52
• Please do not use edit statements, they carry no information whatsoever for anyone who encounters the question for the first time. Use the edit function to improve your post, but still let it read consistently as one post (as if you were writing it for the first time). For those who are interested in the becoming of the post, there is an edit history available. – Martin - マーチン Oct 5 '17 at 12:18

As you say you are starting with Gibbs free energy, just pay attention to the $\Delta G$ values. Remember that $\Delta G= \Delta H -T\Delta S$ so it doesn't depends only on enthalpy but also on entropy. A process where $\Delta G<0$ is exergonic and in the opposite case it is endergonic.
• Salts that disolve in water are exergonic processes, $\Delta G_\mathrm{disol}<0$.
• Sodium bicarbonate will disolve in vinegar to produce $\ce{CO2}$ (because of the high concentration of acetic acid), it is also exergonic.