Question

Pour 25 ml of aqueous citric acid into a beaker. Then add 3 spatula of calcium carbonate and stir. This is a endothermic or exothermic reation? Discuss.

Q2.The same as first one 25 ml of citric acid then add 3 spatula of calcium carbonate but this time adding sodium bicarbonate (so dium hydrogen carbonate) of spatulas. The reaction of citric acid on calcium carbonate is strange, because it is probably measured as endothermic, although in theory, it should be exothermic. This is contradictory, of course. It is due to something special, and this reaction has something special. It may even be one of the most surprising reactions in the world of simple chemistry. The reason is that the reactionCaCOX3CaCOX3+ citric acid produces an improbable clear solution of calcium citrate, and should not, as the different calcium citrates are all nearly insoluble in water. This shows that the obtained clear solution is not a usual solution. It is a supersaturated solution of calcium citrate. If this solution is kept in a closed bottle at room temperature, it will deposit a large amount of calcium citrate as white precipitate after about two days (and not before). Supersaturation is a known phenomena, that rarely lasts long. This clear solution is probably one of the supersaturated solutions which require a long delay before producing spontaneously an insoluble compound. This strange phenomena has been recently studied in detail by Martina Vavrilova, Spontaneous Supersaturation of Calcium Citrate, RSC Adv. 2017, 7, 3078 - 3088, DOI : 10-1039/C6RA258076. As a consequence, the reactionCaCOX3CaCOX3+ citric acid is endothermic when it produces a supersaturated solution of insoluble calcium citrate. The precipitation of calcium citrate out of this supersaturated solution is exothermic.

Answer 1

The reaction between citric acid and calcium carbonate in the creation of a supersaturated solution of calcium citrate is endothermic, absorbing energy from the surroundings. This particular behavior is an exception to the expected exothermic reaction of an acid with a carbonate, due to the unique properties of calcium citrate's solubility.

Step-by-step explanation:

When citric acid reacts with calcium carbonate, it is a reaction that can seem contradictory. Typically, we might expect an acid reacting with a carbonate to be exothermic, with the surroundings getting warmer due to the release of energy.

However, the reaction between citric acid and calcium carbonate producing a supersaturated solution of calcium citrate is actually endothermic, absorbing energy and making the surroundings get cooler. This unique behavior is due to the formation of a supersaturated solution which can spontaneously precipitate calcium citrate after some time—an exothermic process.

The reaction of citric acid with calcium carbonate, with the formation of a supersaturated solution, highlights the complex interplay of thermodynamics and solubility in chemical reactions.