# Chemical Reactions

ChemistryChemical Reactions and Equations

#### Basic Principles of Organic Chemistry

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#### Electro Chemistry

13 Lectures 2 hours

## Introduction

In order to understand the chemical reactions, it is required to understand the definition of chemical and physical change. There lies a vast difference between chemical and physical changes. In chemical change, the molecular composition drastically changes and leads to the formation of a completely new element. It is to be noted that chemical change is irreversible in nature and is permanent. On the other hand, physical change is characterized by significant alterations that are noticed within the arrangement of molecules' 'that result in a change in the state.

## What is a Chemical reaction?

Chemical reaction is a kind of reaction, where molecular bonds are broken down among the molecules that are playing the role of a reactant within the process (Hirai et al. 2020). This further results, in the formation of new bonds among the product molecules leading to the form of a new substance.

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Figure 1: Chemical reactions

## Concepts of chemical reaction

Certain basic concepts are there for the notion of chemical reactions' ', that includes the following. In a chemical reaction, two molecules' ' tend to interact with each other in order to form a new product or product. The compounds that are reacting with each other are known as reactants and the formed new compounds and elements are known as products (Zhan et al. 2018).

In this reaction, the processes occur between any two ions or atoms or molecules leading to the formation of new bonds. However, in chemical reactions, no atoms are destroyed, as well as created. The rate of chemical reactions depends on a number of factors, such as, temperature, pressure, concentration and many more.

## Chemical equations

As there are various chemical reactions happening all around us in a simultaneous nature, creating difficulty in expression. Therefore, for the development of nomenclature, the process of simplification is conducted, such reactions are known as, chemical equations (Visionlearning, 2022). Chemical equations can be expressed as, A + B ${\rightarrow}$ C +D, where, A and B are known as reactants and C and D are the products.

## Types of Chemical reactions

There are in total, six types of chemical reactions, of them only four are considered the most important. However, the reactions include, combustion reaction, decomposition reaction, redox reaction, neutralization reaction, double displacement or precipitation reaction and lastly, synthesis reaction.

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Figure 2: Types of Chemical reactions

## Combustion reaction

Combustion reaction occurs when with an oxidiser a material of combustion acts together to form an oxidized product. However, in this reaction oxygen is allowed to burn in order to accelerate the reaction. For example, such reaction is, ${2\:Mg +O_2\rightarrow 2MgO+Heat}$.

## Decomposition reaction

In a reaction where a single element tends to undergo several breakdowns, resulting in the formation of several products is known as a decomposition reaction. However, during this reaction, changes are to be conducted within the environment such as light or heat, resulting in the breaking up of bonds. For example, such a reaction is, ${CaCO_3 \rightarrow CaO+CO_2}$.

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Figure 3: Decomposition reaction

## Reaction of neutralization

The reaction of neutralization occurs when the water and salt are produced in reaction with acid and bases". However, the molecules of water that are formed are with the combination of ${OH^{-}}$ and ${OH^{+}}$ ions. For example, such reaction is, ${HCl + NaOH \rightarrow NaCl + H_2O}$" (Chem.libretexts, 2022). In this reaction, the resultant common salt and water molecules are formed while reacting with the hydrochloric acid and sodium hydroxide.

## Redox reaction

Redox reaction, better to be known as reduction and oxidation occurs when there lays an exchange of electrons among the chemical elements (Thoughtco, 2022).

For example, ${Zn+2H+\rightarrow Zn2 + +H_2}$ shows a reaction between zinc and hydrogen, resulting in the formation of stable molecules of hydrogen.

## Double displacement reaction

Double displacement reaction or precipitation occurs when a reaction occurs between two compounds resulting in the method of displacement. In this reaction, the anions and the cations seem to change their place resulting in the formation of new products.

For example, ${AgNO_3+NaCl \rightarrow AgCl +NaNO_3}$ ,where, sodium chloride reacts with silver nitrate.

## Synthesis reaction

In the synthesis reaction, the combination occurs for multiple numbers of compound products resulting in the formation of a more complex product. However, it needs to be noted that the combination occurs under specific physical conditions, for example, the reaction between sodium and chloride gas. This reaction can be expressed as, ${2Na + Cl_2 \rightarrow 2NaCl}$

## Conclusion

In this tutorial, the concepts of chemical reactions are discussed with their types and methods. However, before understanding the chemical reactions, it is important to clear the concepts associated with physical and chemical change. It is understood that chemical change is a permanent change that results in the formation of new products, whereas, physical change is considered to be, a temporary change. The physical change results in the changes in the arrangement of the atoms or molecules within the compounds.

Q1. What is meant by chemical combustion reaction?

The process of chemical combustion reaction is a chemical reaction, when a substance undergoes combustion within the presence of air in order to produce heat and light is known as chemical combustion. The substance which is going under such a reaction is known as, combustible.

Q2. What is an equilibrium constant?

In the field of chemistry, equilibrium constant is defined as the numbers that show a relationship between, net amounts of reactants and products within an equilibrium state at a stated equilibrium, in a reversible reaction.

Q3. What is meant by single displacement or substitution reaction?

Substitution reaction, is a reaction when one element is being displaced from a compound element by another respective element. However, it can be displayed as, ${A+BC \rightarrow AC+B}$ It can be shown by an example when zinc is reacted with hydrochloric acid and within the reaction; the element of zinc replaces the hydrogen. This reaction is expressed as, ${Zn +2HCl \rightarrow ZnCl_2 +H_2}$

## Reference

### Journals

Hirai, K., Hutchison, J. A., & Uji-i, H. (2020). Recent progress in vibropolaritonic chemistry. ChemPlusChem, 85(9), 1981-1988. Retrieved from: https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cplu.202000411

Zhan, C., Chen, X. J., Yi, J., Li, J. F., Wu, D. Y., & Tian, Z. Q. (2018). From plasmon-enhanced molecular spectroscopy to plasmon-mediated chemical reactions. Nature Reviews Chemistry, 2(9), 216-230. Retrieved from: https://www.nature.com/articles/s41570-018-0031-9

### Websites

(Inorganic_Chemistry)/Chemical_Reactions/Chemical_Reactions_Examples/Chemical_Reactions_Overview [Retrieved on, ${27^{th}}$ June 2022]
Chem4kids, (2022), Chemical reaction, Retrieved from: http://www.chem4kids.com/files/react_intro.html [Retrieved on, ${27^{th}}$ June 2022]
Thoughtco, (2022), Chemical reaction, Retrieved from: https://www.thoughtco.com/types-of-chemical-reactions-604038 [Retrieved on, ${27^{th}}$ June 2022]