Synthesis reaction: types, factors, examples

In a generic way it can be represented with the form: A + B → C. In a simple synthesis reaction, one reagent A reacts with another reagent B to produce a product C. It is said to consist of a single step. However, it may happen that A must react first with E, followed by F, and finally with G (other reagents), to become the product C; that is, the same reaction takes place in multiple steps.

Regardless of whether it is a single step or many, all synthesis reactions are based on the effectiveness (thermodynamics and kinetics) with which the reactants react to become products, as well as on the experimental performance. It is desired that a synthesis reaction proceed successfully and produce as many products as possible.

Types of synthesis reactions

Single or multiple

Synthetic reactions are not entirely easy to classify. It may be a matter related to the chemist’s judgment. Why? Suppose again the multiple reaction discussed above:

A + E → P 1

1 + F → P 2

2 + G → C

Being P 1 and P 2 intermediate products that are not of interest. The synthesis reaction of the product or compound C, starting from A as the main reagent (limit or limiting reagent), is multiple or complex, since it occurs in several steps, in which other reagents participate: E, F and G.

A) Yes:

A + E → P 1

It can be seen as a simple synthesis reaction for product P 1 , regardless of what type of reaction it is. And likewise:

1 + F → P 2

It is another simple synthesis reaction for product P 2 .

Inorganic or organic

Synthetic reactions can be of any type as regards the nature of the reaction and its molecular mechanism. However, these can be divided according to the chemical nature of the reactants and products.

For example, if the reagents are inorganic substances, then we speak of inorganic syntheses; whereas if they were organic substances, we would already speak of organic syntheses.

Factors involved in synthesis reactions

The factors that intervene in the synthesis reactions are all those parameters or variables, physical and chemical, that directly affect the performance of the reaction and the quality of the products produced. Some of them are the following:


Temperature is paramount in any synthesis reaction. Depending on its thermodynamics, it may be desirable to keep it low or high. Likewise, there are temperature ranges where undesirable side reactions are likely to occur, so it is essential to control and verify it at all times.


Time is also of the essence in synthesis reactions, as it must be ensured that it is long enough to guarantee the establishment of equilibrium. After a certain amount of time, more product will stop being obtained, and that is when it is decided to stop the synthesis completely.

Reagent concentrations and quality

The more concentrated the reagents are, the faster the reactions between them. However, it is also essential to be clear about the proportion of their concentrations, as well as their magnitudes, since the minimum change will affect the final performance.

On the other hand, the reagents must be as pure as possible, otherwise erroneous concentrations will be assumed; Or worse still, products will be contaminated, or undesirable reactions will occur.


How the reaction medium is stirred will influence the rates of synthesis reactions.


Pressure, like concentration, plays a crucial role, especially when the reactants are species or gaseous substances. The higher the pressure, the greater the collisions or interactions between the reactants, and therefore the more likely they are to react.


The pH (acidic or basic) directly affects the mechanism of a reaction, so it is a key factor in defining which products will be obtained at the end of the synthesis.


Catalysts are substances that accelerate chemical reactions but are not consumed during the process. There are syntheses that without your intervention it would be impossible to perform them with an acceptable yield, or it would take a long time to obtain the products.

Examples of synthesis reactions

Next, and finally, the chemical equations for the synthesis reactions of various compounds will be cited.

Table salt (sodium chloride)

This salt is one of the best known by all for its great domestic use. It is obtained from sodium and chlorine, and although it can be obtained by the following reaction, it is very easy to find it naturally.

2 Na + Cl  2  → 2 NaCl


This is one of the most important reactions for life as we know it to exist. The plants use carbon dioxide and water from the environment with sunlight to produce glucose and oxygen.

The reaction in a very general way can be seen below, but it is important to understand that behind it there are several reactions and mechanisms to make this possible.

6CO2 + 6H2O → C6H12O6 + O2


This synthesis reaction occurs in living organisms and occurs by polymerizing glucose with fructose. Due to their structure, these two molecules interact and the end result is sucrose and water, as can be seen in the following equation:

C6H12O6 + C6H12O6 → C12H22O11 + H2O


3 H 2 (g) + N 2 (g) → 2 NH 3 (g)

The reactants H 2 and N 2 are gaseous. The pressure must be high for its molecules to react and originate ammonia, NH 3 . It is one of the most important synthesis reactions in industrial chemistry.


2 H 2 (g) + O 2 (g) → 2 H 2 O (g)

2 and O 2 react exothermically to produce water vapor. The amount of energy released is such that hydrogen is one of the most promising fuels in aerospace applications.


2 H 4 (g) + H 2 O (l) → CH 3 CH 2 OH (l)

Ethanol is known as alcohol, being actually just one of the many alcohols that exist. Its synthesis reaction consists of the hydration of ethylene, C 2 H 4 or H 2 C = CH 2 , where a water molecule is added to its double bond.

Sulfuric acid

Sulfuric acid has several efficient synthetic routes. However, the simplest consists of several steps:

S (s) + O 2 (g) → SO 2 (g)

2 SO 2 (g) + O 2 (g) ⇌ 2 SO 3 (g)

SO 3 (g) + H 2 O (l) → H 2 SO 4 (g)

2 SO 4 (g) → H 2 SO 4 (l)

Sulfur burns with excess oxygen to transform first into SO 2 , then SO 3 . The SO 3 is then hydrated to produce H 2 SO 4 vapors , which finally condense into liquid H 2 SO 4 . This synthesis is so important that it alone indicates how strong an entire nation’s output is.


CO (g) + 2 H 2 (g) → CH 3 OH (l)

The gases CO and H 2 react and condense on metallic catalysts to give rise to methanol, the simplest alcohol of all.

Magnesium sulphate

It can be produced from a very simple reaction consisting of magnesium and sulfuric acid. It is very difficult to find it in nature without water.

Mg + H2SO4 → H2 + MgSO4

Carbon dioxide

It happens naturally in several processes, when the diatomic oxygen molecule meets carbon, carbon dioxide is produced.

It is present in natural processes such as respiration, as a reagent in photosynthesis and is easily produced in combustion reactions.

C + O2 → CO2

Hydrochloric acid

Hydrochloric acid is widely used as a cheap acid and as a reactive agent for the synthesis of other compounds.

Cl2 + H2 → 2HCl

Calcium carbonate

It is widely known as a very abundant agent in nature, mainly in rocks, minerals and shells in the sea. Its reaction is based on the interaction of calcium oxide with carbon dioxide.

CaO + CO2 → CaCO3

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