Chemical_reaction - Wikiparency

# Chemical reaction A **chemical reaction** is a process that transforms one set of substances, the reactants, into another, the products, by breaking and forming [[Chemical_bond|chemical bonds]] and moving [[Electron|electrons]] while leaving every atomic nucleus as it was. Rusting [[Iron|iron]], a burning match and [[Photosynthesis|photosynthesis]] in a leaf are chemical reactions; the decay of a radioactive nucleus is not, because it changes the [[Chemical_element|element]]. Two rules bound every reaction: mass is conserved, since the [[Atom|atoms]] are only rearranged, and electric charge is conserved, since electrons are only transferred.[^af2e-7-1] A reaction is written as a [[Chemical_equation|chemical equation]] whose coefficients enforce both rules; how fast it runs is its [[Chemical_kinetics|kinetics]] and how far it can go its [[Chemical_thermodynamics|thermodynamics]]. In the microsim below the reader balances an equation by hand. For the combustion of propane, C₃H₈ + O₂ → CO₂ + H₂O, four sliders set the four coefficients and three pairs of bars count the [[Carbon|carbon]], [[Hydrogen|hydrogen]] and [[Oxygen|oxygen]] atoms on each side; the bars match only at 1 : 5 : 3 : 4, which is the first rule as a picture. A second preset, copper with silver nitrate, adds a charge bar to each side, so the equation balances only when the electrons [[Copper|copper]] loses equal the electrons [[Silver|silver]] gains, which is the second rule. On the [[Chemistry]] flagship this article opens Part VI — Reaction, section *Reaction* (row K31), as the sibling of the [[Stoichiometry|stoichiometry]] row: that sim turns a balanced equation into masses, this one shows why it must balance first. ## History Fire, fermentation and smelting were used for millennia before anyone knew what a reaction was; [[Alchemy|alchemy]] classified changes by appearance and product. [[Robert_Boyle|Robert Boyle]]'s *Sceptical Chymist* of 1661 argued for elements defined by experiment, and [[Antoine_Lavoisier|Antoine Lavoisier]]'s *Traité élémentaire de chimie* of 1789 made the balance the arbiter: mass is conserved, so a reaction is an equation in which what goes in must come out.[^boyle1661][^lavoisier1789] [[John_Dalton|John Dalton]]'s atomic theory of 1808 explained why compounds have fixed proportions, and Berzelius's letter symbols of 1813–1814 gave equations their notation.[^dalton1808][^berzelius1813] Guldberg and Waage's law of mass action of 1864 tied the position of equilibrium to concentrations; van 't Hoff's *Études de dynamique chimique* of 1884 founded chemical kinetics; and Arrhenius's 1889 paper on the inversion of cane sugar gave the exponential temperature dependence of rate that carries his name.[^guldberg-waage1864][^vanthoff1884][^arrhenius1889] In the twentieth century [[Fritz_Haber|Fritz Haber]]'s synthesis of [[Ammonia|ammonia]] from its elements, recognised with the 1918 Nobel Prize in Chemistry, showed that a reaction could be engineered from thermodynamics and kinetics together; Eyring's transition-state theory of 1935 put the rate constant on a statistical footing; and femtosecond lasers let Ahmed Zewail watch bonds break in real time, work honoured with the 1999 Nobel Prize in Chemistry.[^haber-nobel][^eyring1935][^zewail-nobel] ## Characteristics A chemical change differs from a physical one in that the substances present at the end are not those present at the start: dissolving salt in water is physical, because evaporation gives the salt back, while burning [[Fuel|fuel]] is chemical, because no cooling gives the fuel back. The signs of a reaction are a change of colour, the release or absorption of [[Heat|heat]], the evolution of a gas, the formation of a solid from a solution, or a change in [[Absorbance|absorbance]] or electrical conductivity, but the definitive test is that the products have different properties from the reactants and cannot be recovered by reversing the physical conditions alone. Reactions release or absorb energy — [[Exothermic_reaction|exothermic]] or [[Endothermic_process|endothermic]] — because the bonds broken and the bonds formed store different amounts of it; they run at rates from femtoseconds to geological ages; and they stop, if they stop at all, at an [[Chemical_equilibrium|equilibrium]] in which forward and reverse rates are equal. ## Equations A chemical equation lists the reactants on the left, the products on the right and, before each formula, a coefficient that states how many molecules or formula units take part. Balancing means choosing coefficients so that each element appears the same number of times on both sides; a formula is never altered, since that would change the substance, only the coefficient before it.[^af2e-7-1] The microsim's first preset is the burning of propane: with the coefficients 1, 5, 3, 4 the carbon bars read 3 and 3, the hydrogen bars 8 and 8, and the oxygen bars 10 (from five O₂) and 10 (six in three CO₂ plus four in four H₂O). Any other setting leaves a pair unequal, shown in red. Multiplying all four coefficients by the same number balances too, so the convention is the smallest whole-number set.[^af2e-7-1] The [[Mole_(unit)|mole]] turns the coefficient ratio into a mass ratio: 44.10 g of propane and 159.99 g of oxygen become 132.03 g of carbon dioxide and 72.06 g of water, 204.09 g in and 204.09 g out (derived from the atomic masses), which is [[Conservation_of_mass|conservation of mass]] as arithmetic.[^af2e-7-1][^ball-ch4] The second preset, Cu + AgNO₃ → Cu(NO₃)₂ + Ag, balances by atoms at 1 : 2 : 1 : 2, but the sim also writes the net ionic form Cu + 2 Ag⁺ → Cu²⁺ + 2 Ag and counts charge: +2 on each side, because one copper atom gives up two electrons and each of two silver ions takes one.[^af2e-7-1] That count is what a redox equation adds, and it is why half-reactions are balanced for electrons before they are added. State symbols (s), (l), (g) and (aq) complete the equation, and a double arrow ⇌ marks a reaction that reaches equilibrium. ## Elementary reactions An [[Elementary_reaction|elementary reaction]] happens in a single molecular event, a unimolecular decomposition or a bimolecular collision, and its rate law follows from its molecularity. Most balanced equations are not elementary: the propane equation says nothing about how combustion happens, and the overall change is the sum of a [[Reaction_mechanism|mechanism]] of elementary steps, radical chains in a flame. Rate laws are therefore determined by experiment, never read off a balanced equation unless the step is known to be elementary.[^af2e-rate-law] When an intermediate is short-lived, the [[Steady_state_(chemistry)|steady-state]] approximation sets its net rate of change to zero and yields a rate law whose orders may not even be definable.[^boyd-ssa] ## Chemical equilibrium Many reactions run in both directions, and when the forward and reverse rates become equal the composition stops changing though molecules keep reacting. The [[Equilibrium_constant|equilibrium constant]] K is the ratio of product to reactant concentrations, each raised to its coefficient, at that point; the [[Reaction_quotient|reaction quotient]] Q is the same ratio at any other moment, and the reaction runs forward while Q < K. [[Le_Chatelier's_principle|Le Chatelier's principle]] summarises the response to a disturbance: the equilibrium shifts so as to oppose it. For a reversible elementary step K = k_f/k_r, a ratio of rates as well as of concentrations, and a [[Catalysis|catalyst]], which raises both rates equally, leaves it untouched.[^af2e-catalysis] ## Thermodynamics Whether a reaction can run is decided by the [[Gibbs_free_energy|Gibbs energy]] change ΔG = ΔH − T·ΔS at constant temperature and pressure — negative for a spontaneous forward reaction, positive for the reverse — and ΔG° = −R·T·ln K ties the standard value to the equilibrium constant.[^af2e-12-4] The [[Enthalpy|enthalpy]] term is the heat measured by [[Calorimetry|calorimetry]], and the propane preset of the microsim is strongly exothermic: burning a hydrocarbon releases about 650 kJ per mole of CH₂ units.[^ball-nuclear] The entropy term decides the cases the enthalpy does not — a cold-pack salt dissolving, limestone decomposing when hot — and the [[Chemical_thermodynamics|chemical thermodynamics]] article works the four sign cases with a temperature slider. Thermodynamics says nothing about time: propane and oxygen have an enormous K at room temperature and sit together indefinitely until a spark supplies the activation energy. ## Kinetics The rate of a reaction is the change of concentration per unit time, and the [[Rate_equation|rate law]], rate = k·[A]^m·[B]^n, gives its dependence on the concentrations through orders m and n that are found by experiment.[^af2e-rate-law] A first-order reaction decays exponentially with a constant [[Half-life|half-life]] of 0.693/k, whatever the starting concentration; a second-order one has a half-life that lengthens as the reactant is used up.[^af2e-integrated] The rate constant k rises steeply with temperature according to the [[Arrhenius_equation|Arrhenius equation]], k = A·exp(−E_a/(R·T)), where E_a is the [[Activation_energy|activation energy]], the barrier between reactants and the [[Transition_state|transition state]]: for the decomposition of hydrogen iodide the rate constant grows from 3.52×10⁻⁷ L/(mol·s) at 555 K to 3.95×10⁻² at 781 K, a factor of 10⁵ over 226 K, which fits E_a ≈ 180 kJ/mol.[^af2e-arrhenius] The everyday version of the same law is that rates roughly double for every 10 °C, which is why food is refrigerated and why a fever matters.[^af2e-rule-of-thumb] ## Reaction types Reactions are grouped by what is rearranged and by the pattern of the rearrangement; the same reaction often belongs to more than one group. ### Four basic types Introductory texts sort reactions into synthesis (A + B → AB), decomposition (AB → A + B), single displacement (A + BC → AC + B) and double displacement (AB + CD → AD + CB).[^ball-ch4] The sim's copper–silver preset is a single displacement; most double displacements in solution are precipitations or acid–base reactions. ### Forward and backward reactions Every reaction can in principle run backward, and the ratio of the two rate constants is the equilibrium constant. Which direction dominates depends on ΔG under the actual conditions, so a reaction that runs forward in a flask can be driven backward in a reactor by removing a product or changing the temperature. ### Oxidation and reduction [[Redox|Oxidation]] is loss of electrons and reduction is gain; the two always occur together, and the [[Oxidation_state|oxidation state]] of each atom tracks them.[^ball-redox] In the sim's second preset copper is oxidised from 0 to +2 and silver reduced from +1 to 0; the two electrons per copper atom are what the charge bar counts. Redox reactions run rusting, [[Combustion|combustion]], [[Electric_battery|batteries]], [[Electrolysis|electrolysis]] and respiration; separated into half-reactions in an [[Electrochemical_cell|electrochemical cell]], their tendency appears as a voltage. ### Combustion Combustion is the rapid redox reaction of a fuel with oxygen, releasing heat and usually light; complete combustion of a hydrocarbon gives carbon dioxide and water, as in the sim's propane equation, while incomplete combustion gives carbon monoxide and soot. It proceeds through radical chains, which is why a flame needs ignition and then propagates. ### Complexation In a complexation reaction a metal ion binds [[Ligand|ligands]] through their lone pairs to form a [[Coordination_complex|coordination complex]]; the ligands split the metal's d orbitals, and the size of the splitting, ordered by the spectrochemical series, sets colour and magnetism.[^boyd-ligand] Complexation is how [[Hemoglobin|hemoglobin]] carries oxygen and how metal ions are extracted and analysed. ### Acid–base reactions An [[Acid–base_reaction|acid–base reaction]] transfers a proton from a Brønsted acid to a base; a strong acid ionises completely in water, while a weak acid such as acetic acid, with K_a = 1.8×10⁻⁵, is only about 1.3 % ionised at 0.10 M.[^af2e-weak-acid] Neutralisation of a strong acid by a strong base, the calorimetry sim's coffee-cup preset, is always the same reaction, H⁺ + OH⁻ → H₂O. ### Precipitation A [[Precipitation_(chemistry)|precipitation]] reaction forms an insoluble solid when two solutions are mixed; the solubility product, the constant of the [[Solubility_equilibrium|solubility equilibrium]] between the solid and its ions, decides whether it happens.[^af2e-ksp] Silver chloride from silver nitrate and sodium chloride is the classic example; precipitation underlies gravimetric analysis and water treatment. ### Solid-state reactions Reactions between solids are limited by [[Diffusion|diffusion]], because atoms must travel through a lattice to meet; they run at high temperature, and their products form by [[Nucleation|nucleation]] at interfaces. The [[Born–Haber_cycle|Born–Haber cycle]] accounts for the formation of an ionic lattice from its elements; its lattice-energy term is what makes MgCl₂, not MgCl or MgCl₃, the stable chloride of magnesium.[^cboc-born-haber] ### Reactions at the solid/gas interface A gas reacting with a solid surface — oxygen with a metal, hydrogen on platinum — proceeds through adsorption, reaction on the surface and desorption, and its rate depends on the surface area and on how strongly each species sticks. Heterogeneous catalysis, corrosion and the growth of oxide films are reactions of this kind. ### Photochemical reactions A [[Photon|photon]] can supply the energy that heat cannot: absorbing light lifts a molecule to an excited state from which bonds break or form that would not in the ground state, and the photon energy h·c/λ sets the threshold, as in the [[Photoelectric_effect|photoelectric effect]].[^cboc-photon] Photosynthesis, vision and the formation and destruction of stratospheric [[Ozone|ozone]] are photochemical. ## Catalysis A catalyst speeds a reaction without being consumed, by providing a different mechanism with a lower activation energy; the energies of the reactants and products, and therefore ΔH, ΔG and K, are unchanged.[^af2e-catalysis] The Portal Book's example compares two paths for the same two-step reaction, with first-step barriers of 80 and 70 kJ/mol, and a 10 kJ/mol drop at 298 K speeds a reaction some 57-fold (derived from the Arrhenius factor).[^af2e-catalysis-ex] [[Enzyme|Enzymes]] are biological catalysts, [[Michaelis–Menten_kinetics|saturable]] and specific; industrial catalysts such as the iron of ammonia synthesis are solids working at the solid/gas interface. ## Reactions in organic chemistry [[Organic_chemistry|Organic]] reactions are sorted by what happens to the carbon skeleton and by mechanism, the movement of electron pairs or single electrons. ### Substitution In a substitution one group on a carbon is replaced by another; the nucleophile can attack as the leaving group departs in one concerted step, or the leaving group can depart first to give a carbocation that the nucleophile then captures, and the two mechanisms differ in kinetics, stereochemistry and solvent sensitivity. ### Addition and elimination Addition breaks a double or triple bond and attaches two new groups across it, converting an alkene to an alkane, alcohol or halide; elimination is the reverse and creates the multiple bond. Together they are how [[Polymer|polymers]] are built from alkenes and how alkenes are made from alcohols. ### Other organic reaction mechanisms Radical reactions proceed through species with an unpaired electron; pericyclic reactions rearrange bonds through a cyclic transition state in one step; and rearrangements move a group from one carbon to another within the molecule. [[Quantum_chemistry|Quantum chemistry]] now routinely maps the energy surface of a proposed mechanism. ## Biochemical reactions The reactions of life are the same reactions run under mild conditions by enzymes: [[Cellular_respiration|cellular respiration]] oxidises glucose to carbon dioxide and water in dozens of coupled steps, capturing the energy as [[Adenosine_triphosphate|ATP]], whose hydrolysis drives biosynthesis; photosynthesis runs the same redox chemistry in reverse with light.[^af2e-12-4] Every step obeys the microsim's balancing rules; metabolic pathways are long chains of balanced equations. ## Applications The [[Chemical_industry|chemical industry]] runs reactions at scale: ammonia synthesis for fertiliser, the [[Chloralkali_process|chloralkali process]] for chlorine and sodium hydroxide, [[Electrolysis|electrolysis]] for aluminium, cracking and polymerisation for fuels and plastics, and multistep syntheses for medicines. [[Materials_science|Materials science]] uses reactions to make [[Steel|steel]], [[Ceramic|ceramics]] and [[Semiconductor|semiconductors]] and to control [[Corrosion|corrosion]]; energy technology uses them in [[Fuel_cell|fuel cells]] and [[Lithium-ion_battery|lithium-ion batteries]]. In every case the balanced equation is the first line of the design, because it fixes the [[Stoichiometry|stoichiometry]] from which yields, costs and waste follow. ## Monitoring A reaction is followed by measuring a property that changes as it runs. [[Spectroscopy|Spectroscopy]] is the commonest probe — a colour change by [[Ultraviolet–visible_spectroscopy|UV–visible]] absorbance through the [[Beer–Lambert_law|Beer–Lambert law]], a bond change by [[Infrared_spectroscopy|infrared]] or [[Nuclear_magnetic_resonance|NMR]] — and [[Mass_spectrometry|mass spectrometry]] and [[Chromatography|chromatography]] identify and quantify intermediates and products. Temperature, pressure, conductivity and [[PH|pH]] are logged continuously in industrial reactors, and [[Titration|titration]] of samples withdrawn at intervals is the classical kinetic method. The rate laws of the kinetics section are fitted to exactly such time series.[^af2e-rate-law] ## See also - [[Chemical_equation]] - [[Conservation_of_mass]] - [[Reaction_mechanism]] - [[Elementary_reaction]] - [[Chemical_synthesis]] - [[Combustion]] - [[Stoichiometry]] - [[Chemical_kinetics]] - [[Chemical_equilibrium]] ## References [^af2e-7-1]: Flowers, Paul; Neth, Edward; Robinson, William; et al. (2019). *Chemistry: Atoms First 2e*. OpenStax. Chapter 7 "Stoichiometry of Chemical Reactions", §7.1 "Writing and Balancing Chemical Equations" (chapter pp. 313–362; page to pin). https://openstax.org/books/chemistry-atoms-first-2e/pages/7-1-writing-and-balancing-chemical-equations — Portal Book 051, https://open.umn.edu/opentextbooks/textbooks/chemistry-atoms-first [^ball-ch4]: Ball, David W. (2011). *Introductory Chemistry*. Chapter 4 "Chemical Reactions and Equations", pp. 157–215 (balancing; the four basic reaction types; page to pin). Portal Book 056, https://open.umn.edu/opentextbooks/textbooks/introductory-chemistry [^ball-redox]: Ball (2011), *Introductory Chemistry*, Chapter 14 "Oxidation and Reduction", pp. 673–719 (oxidation states; balancing redox equations; page to pin). Portal Book 056. [^ball-nuclear]: Ball (2011), *Introductory Chemistry*, Chapter 15 "Nuclear Chemistry", p. 753 (≈ 650 kJ/mol per CH₂ in hydrocarbon combustion). Portal Book 056. [^af2e-rate-law]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17 "Kinetics", pp. 799 and 804 (rate = k[A]^m[B]^n; orders determined by experiment, not by stoichiometry). Portal Book 051. [^af2e-integrated]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17, pp. 806 and 813–815 (first-order half-life 0.693/k; second-order half-life 1/(k[A]₀)). Portal Book 051. [^af2e-arrhenius]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17, pp. 819–821 (k = A·exp(−E_a/RT); HI decomposition data, 555–781 K; E_a = 1.8×10⁵ J/mol). Portal Book 051. [^af2e-rule-of-thumb]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17, p. 784 (rates roughly double per 10 °C). Portal Book 051. [^af2e-catalysis]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17, pp. 828 and 834–835 (a catalyst lowers E_a by a different mechanism; K = k_f/k_r is unchanged). Portal Book 051. [^af2e-catalysis-ex]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 17, pp. 828–829 (Example 17.15: first-step barriers of 80 and 70 kJ/mol on the two paths). Portal Book 051. [^boyd-ssa]: Boyd, W. Christopher (2025). *Exploring Inorganic and Organometallic Chemistry*. Chapter 10, pp. 280–282 (the steady-state approximation; orders that "cannot be specified"). Portal Book 052, https://open.umn.edu/opentextbooks/textbooks/exploring-inorganic-and-organometallic-chemistry [^boyd-ligand]: Boyd (2025), *Exploring Inorganic and Organometallic Chemistry*, Chapter 8 "Ligand Field Theory", pp. 195–211 (octahedral splitting; the spectrochemical series). Portal Book 052. [^af2e-12-4]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 12 "Thermodynamics", §12.4 "Free Energy" (ΔG = ΔH − TΔS; ΔG° = −RT ln K; coupled reactions; chapter pp. 597–622; page to pin). Portal Book 051. [^af2e-weak-acid]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 14 "Acid-Base Equilibria", pp. 675–676 and 684 (0.10 M acetic acid, 1.3 % ionised) and p. 716 (K_a = 1.80×10⁻⁵). Portal Book 051. [^af2e-ksp]: Flowers et al. (2019), *Chemistry: Atoms First 2e*, Chapter 15 "Equilibria of Other Reaction Classes" (chapter pp. 719–752; page to pin) and Appendix J "Solubility Products", pp. 1117–1122. Portal Book 051. [^cboc-born-haber]: Blackstock, Lindsay; Brewer, Sharon; Cinel, Bruno (2022). *Chemical Bonding and Organic Chemistry*. Chapter 4 "Chemical Bonding I", pp. 224–228 (Born–Haber cycles; ΔH_f of MgCl, MgCl₂ and MgCl₃). Portal Book 054, https://open.umn.edu/opentextbooks/textbooks/chemical-bonding-and-organic-chemistry [^cboc-photon]: Blackstock, Brewer and Cinel (2022), *Chemical Bonding and Organic Chemistry*, Chapter 2, pp. 176–180 (E = hc/λ; the photoelectric threshold). Portal Book 054. [^boyle1661]: Boyle, Robert (1661). *The Sceptical Chymist*. London: J. Cadwell for J. Crooke. [^lavoisier1789]: Lavoisier, Antoine (1789). *Traité élémentaire de chimie*. Paris: Cuchet. [^dalton1808]: Dalton, John (1808). *A New System of Chemical Philosophy*, Part I. Manchester: R. Bickerstaff. [^berzelius1813]: Berzelius, J. J. (1813–1814). "Essay on the Cause of Chemical Proportions, and on Some Circumstances Relating to Them: Together with a Short and Easy Method of Expressing Them." *Annals of Philosophy* 2–3. [^guldberg-waage1864]: Guldberg, C. M.; Waage, P. (1864). "Studier over Affiniteten." *Forhandlinger i Videnskabs-Selskabet i Christiania*, 1864. [^vanthoff1884]: van 't Hoff, J. H. (1884). *Études de dynamique chimique*. Amsterdam: Frederik Muller & Co. [^arrhenius1889]: Arrhenius, S. (1889). "Über die Reaktionsgeschwindigkeit bei der Inversion von Rohrzucker durch Säuren." *Zeitschrift für physikalische Chemie* 4: 226–248. [^haber-nobel]: Nobel Prize Outreach. "The Nobel Prize in Chemistry 1918 — Fritz Haber." https://www.nobelprize.org/prizes/chemistry/1918/summary/ [^eyring1935]: Eyring, H. (1935). "The Activated Complex in Chemical Reactions." *Journal of Chemical Physics* 3 (2): 107–115. [^zewail-nobel]: Nobel Prize Outreach. "The Nobel Prize in Chemistry 1999 — Ahmed Zewail." https://www.nobelprize.org/prizes/chemistry/1999/summary/ ## Bibliography - Flowers, Neth, Robinson et al., *Chemistry: Atoms First 2e* (OpenStax, 2019), Chapters 7, 12, 13, 14, 15 and 17 — Portal Book 051, https://open.umn.edu/opentextbooks/textbooks/chemistry-atoms-first - Ball, *Introductory Chemistry* (2011), Chapters 4, 5 and 14 — Portal Book 056, https://open.umn.edu/opentextbooks/textbooks/introductory-chemistry - Boyd, *Exploring Inorganic and Organometallic Chemistry* (2025), Chapters 8 and 10 — Portal Book 052. - Blackstock, Brewer and Cinel, *Chemical Bonding and Organic Chemistry* (2022), Chapters 2, 4 and 7–9 — Portal Book 054. - Averill and Eldredge, *General Chemistry: Principles, Patterns, and Applications* (2011), Chapter 5 (balancing chemical equations; pp. 233–496; page to pin) — Portal Book 050, https://open.umn.edu/opentextbooks/textbooks/general-chemistry-principles-patterns-and-applications  **Microsim — three.js (Wikitube framework), pending deploy:** *Chemical reaction* will play here once `https://wikitube-3d-microsims.netlify.app/matter/Chemical_reaction.html` is live.   ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Chemical_reaction) : [Wikitube](https://en.wikitube.io/wiki/Chemical_reaction) · pinned revision [1367113117](https://en.wikipedia.org/w/index.php?oldid=1367113117) · 2026-09-11 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Chemistry]]. --- *Matter & Energy Cluster child articles, wave 1 · 2026-09-11 · drafted · Chemistry row K31 · sim pending (matter/Chemical_reaction).*