Editing Carbonic acid (section)

==In aqueous solution==
In even a slight presence of water, carbonic acid [[Dehydration reaction|dehydrates]] to [[carbon dioxide]] and [[water]], which then [[Autocatalysis|catalyzes]] further decomposition.<ref name="lo" /> For this reason, carbon dioxide can be considered the carbonic [[Acidic oxide|acid anhydride]].

The [[hydrate|hydration]] [[equilibrium constant]] at 25&nbsp;°C is {{awrap|[{{chem|H|2|CO|3}}]/[{{CO2}}]&nbsp;≈ 1.7×10<sup>−3</sup>}} in pure water<ref name="HS">{{cite book |last1=Housecroft |first1=C.E. |title=Inorganic Chemistry |last2=Sharpe |first2=A.G. |date=2005 |publisher=Prentice-Pearson-Hall |isbn=0-13-039913-2 |edition=2nd |page=368 |oclc=56834315}}</ref> and ≈&nbsp;1.2×10<sup>−3</sup> in [[seawater]].<ref name="SB">{{cite journal |last=Soli |first=A. L. |author2=R. H. Byrne |year=2002 |title=CO<sub>2</sub> system hydration and dehydration kinetics and the equilibrium CO<sub>2</sub>/H<sub>2</sub>CO<sub>3</sub> ratio in aqueous NaCl solution |journal=Marine Chemistry |volume=78 |issue=2–3 |pages=65–73 |doi=10.1016/S0304-4203(02)00010-5}}</ref> Hence the majority of carbon dioxide at geophysical or biological [[Surface water|air-water interfaces]] does not convert to carbonic acid, remaining dissolved {{CO2}} gas. However, the [[catalyst|uncatalyzed]] equilibrium is reached quite slowly: the [[rate constant]]s are 0.039&nbsp;[[Second|s]]<sup>−1</sup> for hydration and 23&nbsp;s<sup>−1</sup> for dehydration.

===In biological solutions===
In the presence of the enzyme [[carbonic anhydrase]], equilibrium is instead reached rapidly, and the following reaction takes precedence:<ref name="Lindskog_1997">{{cite journal |vauthors=Lindskog S |year=1997 |title=Structure and mechanism of carbonic anhydrase |journal=Pharmacology & Therapeutics |volume=74 |issue=1 |pages=1–20 |doi=10.1016/S0163-7258(96)00198-2 |pmid=9336012}}</ref> <chem display=block>HCO3^- {+} H^+ <=> CO2 {+} H2O</chem>

When the created carbon dioxide exceeds its solubility, gas evolves and a third equilibrium <chem display=block>CO_2 (soln) <=> CO_2 (g)</chem> must also be taken into consideration. The equilibrium constant for this reaction is defined by [[Henry's law#Fundamental types and variants of Henry's law constants|Henry's law]]. 

The two reactions can be combined for the equilibrium in solution: <math chem="" display="block">\begin{align}
\ce{HCO3^{-}{} + H+{} <=> CO2(soln){} + H2O} && K_3 = \frac{[\ce{H+}][\ce{HCO3^-}]}{[\ce{CO2(soln)}]}
\end{align}</math> When Henry's law is used to calculate the denominator '''care is needed''' with regard to units since Henry's law constant can be commonly expressed with 8 different dimensionalities.<ref>{{Cite journal |last=Sander |first=Rolf |last2=Acree |first2=William E. |last3=Visscher |first3=Alex De |last4=Schwartz |first4=Stephen E. |last5=Wallington |first5=Timothy J. |date=2022-01-01 |title=Henry’s law constants (IUPAC Recommendations 2021) |url=https://www.degruyter.com/document/doi/10.1515/pac-2020-0302/html |journal=Pure and Applied Chemistry |language=en |volume=94 |issue=1 |pages=71–85 |doi=10.1515/pac-2020-0302 |issn=1365-3075|doi-access=free}}</ref>

=== In water pH control ===
In wastewater treatment and agriculture irrigation, carbonic acid is used to acidify the water similar to [[sulfuric acid]] and [[sulfurous acid]] produced by sulfur burners.<ref>{{Cite web |last=Meneses |first=Adolfo |date=November 19, 2024 |title=Irrigation water acidification using captured CO2; An option to traditional acidification systems. |url=https://www.worldagexpo.com/wp-content/uploads/sites/2/2020/11/Soil-acidification-r.-1.0.pdf |access-date=November 19, 2024 |website=World Ag Expo}}</ref>

=== Under high CO<sub>2</sub> partial pressure ===
In the [[beverage industry]], sparkling or "fizzy water" is usually referred to as [[carbonated water]]. It is made by dissolving carbon dioxide under a small [[positive pressure]] in water. Many [[soft drink]]s treated the same way [[effervescent|effervesce]].

Significant amounts of molecular {{chem|H|2|CO|3}} exist in aqueous solutions subjected to pressures of multiple [[Gigapascal|gigapascals]] (tens of thousands of atmospheres) in planetary interiors.<ref>{{cite journal |last1=Wang |first1=Hongbo |last2=Zeuschner |first2=Janek |last3=Eremets |first3=Mikhail |last4=Troyan |first4=Ivan |last5=Williams |first5=Jonathon |date=27 January 2016 |title=Stable solid and aqueous H<sub>2</sub>CO<sub>3</sub> from CO<sub>2</sub> and H<sub>2</sub>O at high pressure and high temperature |journal=Scientific Reports |volume=6 |issue=1 |page=19902 |bibcode=2016NatSR...619902W |doi=10.1038/srep19902 |pmc=4728613 |pmid=26813580 |doi-access=free}}</ref><ref>{{cite journal |last1=Stolte |first1=Nore |last2=Pan |first2=Ding |date=4 July 2019 |title=Large presence of carbonic acid in CO<sub>2</sub>-rich aqueous fluids under Earth's mantle conditions |journal=The Journal of Physical Chemistry Letters |volume=10 |issue=17 |pages=5135–41 |arxiv=1907.01833 |doi=10.1021/acs.jpclett.9b01919 |pmid=31411889 |s2cid=195791860}}</ref> Pressures of 0.6–1.6&nbsp;[[gigapascal|GPa]] at 100&nbsp;[[kelvin|K]], and 0.75–1.75&nbsp;GPa at 300&nbsp;K are attained in the cores of large icy satellites such as [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]], and [[Titan (moon)|Titan]], where water and carbon dioxide are present. Pure carbonic acid, being denser, is expected to have sunk under the ice layers and separate them from the rocky cores of these moons.<ref name="Saleh-Scirep">{{cite journal |author1=G. Saleh |author2=A. R. Oganov |date=2016 |title=Novel Stable Compounds in the C-H-O Ternary System at High Pressure |journal=Scientific Reports |volume=6 |page=32486 |bibcode=2016NatSR...632486S |doi=10.1038/srep32486 |pmc=5007508 |pmid=27580525}}</ref>