Editing Chemical reaction (section)

===Forward and backward reactions===
According to [[Le Chatelier's Principle]], reactions may proceed in the forward or reverse direction until they end or reach [[Equilibrium chemistry|equilibrium]].<ref name="libretext1">{{Cite web |date=2016-08-05 |title=8.3: Le Châtelier's Principle |url=https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_8%3A_Properties_of_Solutions/8.3%3A_Le_Ch%C3%A2telier%27s_Principle |access-date=2023-04-11 |website=Chemistry LibreTexts |language=en}}</ref>

====Forward reactions====
Reactions that proceed in the forward direction (from left to right) to approach equilibrium are often called [[spontaneous reaction]]s, that is, <math>\Delta G</math> is negative, which means that if they occur at constant temperature and pressure, they decrease the [[Gibbs free energy]] of the reaction. They require less energy to proceed in the forward direction.<ref name="libretext2">{{Cite web |date=2016-08-05 |title=11.5: Spontaneous Reactions and Free Energy |url=https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_11%3A_Properties_of_Reactions/11.5%3A_Spontaneous_Reactions_and_Free_Energy#:~:text=The%20forward,form. |access-date=2023-04-11 |website=Chemistry LibreTexts |language=en}}</ref> Reactions are usually written as forward reactions in the direction in which they are spontaneous. Examples:
* Reaction of hydrogen and oxygen to form water.
:{{chem|2H|2}} + {{chem|O|2}} {{eqm}} {{chem|2H|2|O}}
* Dissociation of [[acetic acid]] in water into [[acetate]] ions and [[hydronium ion]]s.
:{{chem|CH|3|COOH}} + {{chem|H|2|O}} {{eqm}} {{chem|CH|3|COO|-}} + {{chem|H|3|O|+}}

====Backward reactions====
Reactions that proceed in the backward direction to approach equilibrium are often called [[non-spontaneous reaction]]s, that is, <math>\Delta G</math> is positive, which means that if they occur at constant temperature and pressure, they increase the [[Gibbs free energy]] of the reaction. They require input of energy to proceed in the forward direction.<ref name="libretext2" /><ref name="libretext3">{{Cite web |date=2016-06-27 |title=20.3: Spontaneous and Nonspontaneous Reactions |url=https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/20%3A_Entropy_and_Free_Energy/20.03%3A_Spontaneous_and_Nonspontaneous_Reactions#:~:text=In%20the%20reverse,spontaneous. |access-date=2023-04-11 |website=Chemistry LibreTexts |language=en}}</ref> Examples include:
* Charging a normal DC battery (consisting of [[electrolytic cell]]s) from an external electrical power source<ref>{{Cite web |date=2013-10-02 |title=Electrolytic Cells |url=https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Electrolytic_Cells |access-date=2023-04-11 |website=Chemistry LibreTexts |language=en}}</ref>
* [[Photosynthesis]] driven by absorption of [[electromagnetic radiation]] usually in the form of sunlight<ref>{{Cite web |date=2016-05-26 |title=Photosynthesis of Exoplanet Plants |url=https://chem.libretexts.org/Ancillary_Materials/Exemplars_and_Case_Studies/Exemplars/Physics_and_Astronomy/Photosynthesis_of_Exoplanet_Plants |access-date=2023-04-11 |website=Chemistry LibreTexts |language=en}}</ref>

:{{underset|carbon<br />dioxide|CO<sub>2</sub>}} + {{underset| water |H<sub>2</sub>O}} + {{underset|light energy|photons}} → {{underset|carbohydrate|[CH<sub>2</sub>O]}} + {{underset| oxygen |O<sub>2</sub>}}