Types of Chemical Reactions

Most Chemistry or Science courses require you to know the names of many types of chemical reactions and ask exam questions on this topic. Exactly which types of reaction depends on the course you take. Here I'll show you how to recognise the sort of things they are likely to ask you about. For a named type of reaction, it must fit the description for that type exactly - it must have only the reactants mentioned and form only the products (and all of the products) given. If there is an extra product or reactant, or one of them is missing, then it is not that type of reaction. It is as simple as that. These are popular exam questions, so it is worth learning the definitions very carefully. If the chemical reaction doesn't fit the entire definition, it's not that type of reaction. (But some reactions can fit more than one type.) Enjoy this chemistry tutorial - I hope it helps with your chemistry homework problems.

The main types of chemical reactions

Oxidation and Reduction Acid - Base Acid - Metal oxide Acid - Metal
Acid - Carbonate Esterification Hydrolysis Hydrogenation
Substitution      

 

Oxidation and Reduction

A reaction where one chemical is oxidised and another is reduced.

In simple terms, one substance gains oxygen (or loses hydrogen) and another loses oxygen (or gains hydrogen). This is explained in more detail in the tutorials on this topic on the Main Science Page, which you should read next, especially if you are on an advanced course which uses the electron gain/loss definition. But here are a couple of examples to help you along. There are many examples of this type of reaction in all chemistry courses.

Iron and oxygen ---> iron oxide, where the iron gets oxidised
4Fe + 3O2 ---> 2Fe2O3

Ethanol and oxygen ---> ethanoic acid, where the ethanol gets oxidised
CH3CH2OH + [O] ---> CH3COOH
(the [O] means some other chemical supplies the oxygen)

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Acid - Base

A reaction between an acid and a base to form a salt and water as the only products.

Hydrochloric acid and sodium hydroxide ---> sodium chloride and water
HCl + NaOH ---> NaCl + H2O

Sulphuric acid and potassium hydroxide ---> potassium sulphate and water
H2SO4 + 2KOH ---> K2SO4 + 2H2O

Nitric acid and calcium hydroxide ---> calcium nitrate and water
2HNO3 + Ca(OH)2 ---> Ca(NO3)2 + 2H2O

Ethanoic acid and sodium hydroxide ---> sodium ethanoate and water
(Acetic acid and sodium hydroxide ---> sodium acetate and water , using the older names)
CH3COOH + NaOH ---> NaOOCCH3 + H2O

This is one of the first named reactions most chemistry courses mention, but it has a simple variation, described below.

(If you are not sure about what is an acid and what is a base, visit the Acids and Bases Page.)

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Acid - Metal Oxide

A reaction between an acid and a metal oxide to form a salt and water as the only products.

This is a special example of an acid - base reaction.

Hydrochloric acid and iron oxide ---> iron chloride and water
6HCl + Fe2O3 ---> 2FeCl3 + 3H2O

Sulphuric acid and copper oxide ---> copper sulphate and water
H2SO4 + CuO ---> CuSO4 + H2O

Metal oxides are also bases. Water soluble ones form metal hydroxides in solution, which are the bases in the previous example.

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Acid - Metal

A reaction between an acid and a metal, forming a metal salt and hydrogen as the only products.

Hydrochloric acid and zinc ---> zinc chloride and hydrogen
2HCl + Zn ---> ZnCl2 + H2

Sulphuric acid + magnesium ---> magnesium sulphate and hydrogen
H2SO4 + Mg ---> MgSO4 + H2

Ethanoic acid and calcium ---> calcium ethanoate and hydrogen
(Acetic acid and calcium ---> calcium acetate and hydrogen , using the older names)
2CH3COOH + Ca---> Ca(OOCCH3)2 + H2

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Acid - Carbonate

A reaction between an acid and a carbonate forming a salt, carbon dioxide and water as the only products.

Nitric acid and sodium carbonate ---> sodium nitrate and carbon dioxide and water
2HNO3 + Na2CO3 ---> 2NaNO3 + CO2 + H2O

Sulphuric acid and calcium carbonate ---> calcium sulphate and carbon dioxide and water
H2SO4 + CaCO3 ---> CaSO4 + CO2 + H2O

Hydrochloric acid and calcium carbonate ---> calcium chloride and carbon dioxide and water
2HCl + CaCO3 ---> CaCl2 + CO2 + H2O

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Esterification

A reaction forming an ester.

Usually this is a reaction between an organic acid and and an alcohol forming an ester and water as the only products.
In some more advanced courses, it includes the reaction between an acid chloride and an alcohol to form an ester and HCl gas as the only products.
To help you follow what happens, I've coloured part of the alcohol molecule red to make it easier to trace.

Ethanol and ethanoic acid ---> ethyl ethanoate and water
(or ethanol and acetic acid ---> ethyl acetate and water, to use the old fashioned names from over 30 years ago)
CH3CH2OH + CH3COOH ---> CH3CH2OOCCH3 + H2O

Methanol and propanoic acid ---> methyl propanoate and water
CH3OH + CH3CH2COOH ---> CH3OOCCH2CH3 + H2O

And the more advanced examples.
Methanol and butanoyl chloride ---> methyl butanoate and hydrogen chloride
CH3OH + CH3CH2CH2COCl ---> CH3OOCCH2CH2CH3 + HCl

Methanol and ethanoyl chloride ---> methyl ethanoate and hydrogen chloride
CH3OH + CH3COCl ---> CH3OOCCH3 + HCl

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Hydrolysis

A reaction where water is one of the reactants, and a larger molecule is split into two smaller molecules, one of which has the hydrogen from the water and the other has the OH group from the water.

Just having water present as the solvent does NOT make a reaction hydrolysis. Hydrolysis is actually a special type of substitution reaction.

Phosphorus trichloride and water ---> phosphorous acid and hydrogen chloride
PCl3 + 3H2O ---> H3PO3 + 3HCl (the structure of H3PO3 is actually P(OH)3 )

Methyl propanoate + water ---> methanol and propanoic acid
CH3OOCCH2CH3 + H2O ---> CH3OH + CH3CH2COOH
This example is the reverse of the earlier esterification reaction, and is usually carried out in the presence of potassium or sodium hydroxide, which then react with the acid formed to give the salt of the acid.

Ethanoyl chloride and water ---> ethanoic acid and hydrogen chloride
CH3COCl + H2O ---> CH3COOH + HCl

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Hydrogenation

A reaction where hydrogen is added across a double bond or even a triple bond.

Ethene and hydrogen ---> ethane
CH2=CH2 + H2 ---> CH3CH3

Butene and hydrogen ---> butane
CH2=CHCH2CH3 + H2 ---> CH3CH2CH2CH3

Propyne and hydrogen ---> propene
CH3C=CH + H2 ---> CH3CH=CH2
Adding more hydrogen will eventually produce propane, CH3CH2CH3

Hydrogenation reactions usually involve a catalyst. Raney nickel, platinum or paladium will catalyse the examples given above.

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Substitution

A reaction where one small group in a molecule is replaced by another small group.

This is actually a whole set of related types of reaction, many of which have their own special name. These reactions are very useful for making new chemicals

Ethanol and hydrochloric acid ---> chloroethane and water
(Or ethyl alcohol and hydrochloric acid ---> ethyl chloride and water, using the old names)
CH3CH2OH + HCl ---> CH3CH2Cl + H2O

Bromoethane and sodium hydroxide ---> ethanol and sodium bromide
(Or ethyl bromide and sodium hydroxide ---> ethyl alcohol and sodium bromide using the older names)
CH3CH2Br + NaOH ---> CH3CH2OH + NaBr

Substitution reactions can be a bit confusing at times, as they can sometimes appear to go backwards as well. It depends on what other chemicals are present at the same time to help them go they way we want them to. If you wrote the first example backwards, it would be a hydrolysis reaction.
i.e. CH3CH2Cl + H2O ---> CH3CH2OH + HCl
Often we use a large excess of the chemical supplying the incoming group to force the reaction to go the way we want. So we would use concentrated HCl to force the first example the way we want it to go. If we started with the chloroethane and added lots of water, the HCl formed in the hydrolysis reaction would be very dilute, so the first reaction is overpowered and doesn't occur.
Don't worry if this seems a bit confusing at first, everyone finds it tricky to begin with, especially if Le Chatelier's Principle isn't part of their course - it is usually not part of the very first courses taught at schools.

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