Editing Chemical reaction (section)

==Equations==
[[File:Combustion reaction of methane.jpg|thumb|450px|As seen from the equation {{chem2|CH4 + 2O2 -> CO2 + 2 H2O}}, a coefficient of 2 must be placed before the [[oxygen]] gas on the reactants side and before the [[properties of water|water]] on the products side in order for, as per the law of conservation of mass, the quantity of each element does not change during the reaction.]]

{{main|Chemical equation}}

[[Chemical equation]]s are used to graphically illustrate chemical reactions. They consist of [[chemical formula|chemical]] or [[structural formula]]s of the reactants on the left and those of the products on the right. They are separated by an arrow (→) which indicates the direction and type of the reaction; the arrow is read as the word "yields".<ref>{{cite book|author=Myers, Richard |title=The Basics of Chemistry|year=2009|url=https://books.google.com/books?id=oS50J3-IfZsC |publisher=[[Greenwood Publishing Group]]|isbn=978-0-313-31664-7|page=55}}</ref> The tip of the arrow points in the direction in which the reaction proceeds. A double arrow ({{eqm}}) pointing in opposite directions is used for [[Chemical equilibrium|equilibrium reactions]]. Equations should be balanced according to the [[stoichiometry]], the number of atoms of each species should be the same on both sides of the equation. This is achieved by scaling the number of involved molecules (A, B, C and D in a schematic example below) by the appropriate integers ''a, b, c'' and ''d''.<ref>{{GoldBookRef|title=chemical reaction equation|file=C01034}}</ref>

:{{chem2|''a'' A + ''b'' B -> ''c'' C + ''d'' D}}

More elaborate reactions are represented by reaction schemes, which in addition to starting materials and products show important intermediates or [[transition state]]s. Also, some relatively minor additions to the reaction can be indicated above the reaction arrow; examples of such additions are water, heat, illumination, a [[catalyst]], etc. Similarly, some minor products can be placed below the arrow, often with a minus sign.
[[File:Baeyer-Villiger-Oxidation-V1.svg|thumb|center|750px|An example of organic reaction: [[Baeyer–Villiger oxidation|oxidation]] of [[ketone]]s to [[ester]]s with a [[Peroxy acid|peroxycarboxylic acid]]]]
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[[Retrosynthetic analysis]] can be applied to design a complex synthesis reaction. Here the analysis starts from the products, for example by splitting selected chemical bonds, to arrive at plausible initial reagents. A special arrow (⇒) is used in retro reactions.<ref>{{Cite journal | doi = 10.1039/CS9881700111| title = Robert Robinson Lecture. Retrosynthetic thinking?essentials and examples| journal = Chemical Society Reviews| volume = 17| pages = 111–133| year = 1988| last1 = Corey | first1 = E.J.}}</ref>