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Redox reaction is a type of chemical reaction, and is the result of electron transfer between chemical species. But, all chemical reactions somehow involve electron transfer!

So, are there chemical reactions without electron transfer?

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    $\begingroup$ All chemical reactions involve attractions between nuclei and protons, but that doesn't mean that all chemical reactions involve electrons moving between species (electron transfer.) $\endgroup$ – Jason Patterson Oct 16 '14 at 13:18
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There are many, here are some examples

  • Ion interchange reactions of various types, such as precipitation

    $\ce{NaCl + AgNO3 -> AgCl \downarrow + NaNO3 }$

  • Polar molecule insert/ejection. The most common case is hydrolysis and reverse reactions.

    $\ce{PCl5 + 4 H2O -> H3PO4 + 5 HCl}$

  • Reorganization of bonds between atoms of same type, such as catalytic benzene synthesis from acetylene

    $\ce{3 C2H2 -> C6H6}$

  • Ligand exchange

    $\ce{ [Fe(H2O)6]^{3+} + 6CN- -> [Fe(CN)6]^{3-} + 6 H2O}$

  • polar oligomerization

    $\ce{ H2O + n CH2O -> HO-(-CH2-O-)_{n}-H}$

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  • $\begingroup$ Can you elaborate on why these each are not redox reactions? $\endgroup$ – spacetyper Oct 17 '16 at 17:55
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    $\begingroup$ @spacetyper Just write down the molecules involved and produced and write down all oxidation states. $\endgroup$ – permeakra Oct 17 '16 at 19:09
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Yes, there are precipitation reactions (which don't have electron transfer), e.g. silver cation and chloride anion combining to make silver chloride, a slightly soluble compound. Also barium sulfate will precipitate.

Hydrolysis of polysaccharides and proteins: with the assistance of enzymes, water is use to break up polysaccharides into simple sugars.

There are others.

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    $\begingroup$ Well it sort of depends on how you define electron transfer. $\endgroup$ – Dissenter Oct 16 '14 at 3:02
  • $\begingroup$ @Dissenter Silver chloride is still a salt, a cation and an anion; there is no transfer of electrons. $\endgroup$ – LDC3 Oct 16 '14 at 3:16
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Of course there are non-redox reactions, for example, acid-base reactions. They do not involve any electron transfer only protons move around (so no oxidation numbers change). Here are some basic examples:

$$ \begin{align} \ce{HCl + H2O &<=> Cl- + H3O+}\\ \ce{HNO3 + H2O &<=> NO3- + H3O+}\\ \ce{CH3-COOH + H2O &<=> CH3-COO+ + H3O+}\\ \ce{HCOOH + H2O &<=> HCOO- + H3O+}\\ \ce{HCl + NaOH &<=> NaCl + H2O} \end{align} $$

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Since redox is defined as gain or loss of electron or electron density it is impossible to have a non-redox reaction. If a reacting species must bond with a different species post-reaction, the electron density must shift due to differences in electronegativity.

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  • $\begingroup$ " it is impossible to have a non-redox reaction. " Three answers above yours demonstrate several examples of non-redox reactions, while you say they're impossible. It'd help if you describe how each of their examples is wrong. $\endgroup$ – Gaurang Tandon Apr 11 '18 at 3:18

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