Do non-redox reactions exist?

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?

• 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.) – Jason Patterson Oct 16 '14 at 13:18

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

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

• Can you elaborate on why these each are not redox reactions? – spacetyper Oct 17 '16 at 17:55
• @spacetyper Just write down the molecules involved and produced and write down all oxidation states. – permeakra Oct 17 '16 at 19:09

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.

• Well it sort of depends on how you define electron transfer. – Dissenter Oct 16 '14 at 3:02
• @Dissenter Silver chloride is still a salt, a cation and an anion; there is no transfer of electrons. – LDC3 Oct 16 '14 at 3:16

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}

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.

• " 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. – Gaurang Tandon Apr 11 '18 at 3:18