You have landed on the right page to learn about Chemical Reactions and Equations. Every living thing born into this magnificent earth has its own unique manner of life. Have you ever looked at your daily life through the eyes of a chemist and analysed it? Chemical reactions take place all around us, including inside our bodies. You may have noticed that iron rusts when it is exposed to the elements for a lengthy period of time.

Similarly, raw vegetables become cooked vegetables when we cook them. The production of new compounds with diverse chemical characteristics occurs in this case. As a result, the rusting of iron is a chemical reaction. Read the article to learn about chemical processes, equations, their types, characteristics, etc. Continue reading to know more.

Chemical Reaction

Chemical reactions are the process in which new substances with new properties are formed. Chemical reactions involve chemical change. During a chemical reaction, atoms of one element do not change into those of another element. A chemical reaction only involves the rearrangement of atoms. Reactants are converted into products in a chemical reaction. The properties of the products formed are entirely different from those of the reactants.

1. The substances which take part in a chemical reaction are called reactants.
2. The new substances produced as a result of a chemical reaction are called products.

For example, the burning of magnesium in the air to form magnesium oxide is an example of a chemical reaction. When a magnesium ribbon is heated, it burns in the air with a dazzling white flame to form magnesium oxide, a white powder. When heated, magnesium reacts with the oxygen in the air to form magnesium oxide.

Characteristics of Chemical Reactions

In a chemical reaction, the conversion of reactants into products is frequently accompanied by some easily observed features. The easily observable features that occur as a result of chemical reactions are known as characteristics of chemical reactions. The following are essential characteristics of chemical reactions:

1. Evolution of gas
2. Formation of precipitate
3. Change in temperature
4. Change in colour
5. Change in taste

CLEAR YOUR CONCEPTUAL DOUBTS ON CHEMICAL REACTIONS

Chemical Equations

A chemical equation represents a chemical reaction using symbols and formulae of the substances involved.

To better understand the meaning of a chemical equation, consider the following example.

Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This reaction can be written as,

\(\text {Zinc}+ \text {Sulphuric acid} \rightarrow \text {Zinc sulphate} + \text {Hydrogen gas}\)

This is known as a word equation. By writing the symbols and formulae of the various substances in place of their names, we can convert this word equation into a chemical equation.

Now, we know that the symbol of zinc is \(\text {Zn}\)

The formula of sulphuric acid is \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

The formula of zinc sulphate is \(\mathrm{ZnSO}_{4}\)

And, formula of hydrogen is \(\mathrm{H}_{2}\)

So, if we put the symbols and formulae of all the substances in the above word- equation, we get the chemical equation shown below.

Balanced and Unbalanced Chemical Equations

Balanced Chemical Equation

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.

For example, zinc reacts with dilute sulphuric acid to give zinc sulphate and hydrogen. This reaction can be written as

\(\mathrm{Zn}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{ZnSO}_{4}+\mathrm{H}_{2}\)

Now count the number of atoms of all the elements in the reactants and products separately;

	In reactants	In products
Number of \(\text {Zn}\) atoms	\(1\)	\(1\)
Number of \(\text {H}\) atoms	\(2\)	\(2\)
Number of \(\text {S}\) atoms	\(1\)	\(1\)
Number of \(\text {O}\) atoms	\(4\)	\(4\)

From the above data, we can say that there are equal atoms of different elements in the reactants and products. So, the above chemical equation is a balanced equation. 

Unbalanced Chemical Equation

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products.
For example, hydrogen reacts with oxygen to form water. This reaction can be written as;

\(\mathrm{H}_{2}+\mathrm{O}_{2} \longrightarrow \mathrm{H}_{2} \mathrm{O}\)

Let us count the number of hydrogen atoms and oxygen atoms in the reactants as well as product;

	In reactants	In products
Number of \(\text {H}\) atoms	\(2\)	\(2\)
Number of \(\text {O}\) atoms	\(2\)	\(1\)

From the above data, we can say that there is an unequal number of atoms of different elements in the reactants and products. Since the number of atoms of various elements in reactants and products is unequal, we can say that an unbalanced equation has unequal masses of various elements in reactants and products.

Balancing of Chemical Equation

The process of making the number of different types of atoms on both sides of an equation equal is known as equation balancing. The hit-and-trial method is used to balance the simple equations.

Following are the four steps for writing equations for the chemical reactions:

1. Write down the chemical reaction as a word equation, with the reactants on the left side and the products on the right.
2. Put the symbols and formulae of all the reactants and products in the word equation. 
3. Balance the equation by multiplying the symbols and formulae by the smallest number of digits possible (Do not change the formulae to balance the equation).
4. If possible, make the equation more informative by indicating the physical states of the reactants and products, the heat changes that occur in the reaction, and the conditions under which the reaction occurs. This step may be skipped if you do not have enough information about the physical states, heat changes, and reaction conditions.

Types of Chemical Reactions

Chemical reactions cause bonds in the reacting species to break and new bonds to form in the resultant species. Chemical reactions can include the interchange of partners in a variety of ways, resulting in a variety of reactions. The various forms of chemical reactions are described in the following sections.

1. Combination Reaction

Two or more substances combine to form a single substance are called combination reactions. In a combination reaction, two or more elements can combine to form a compound; two or more compounds can form a new compound, or an element and a compound can combine to form a new compound.

For example, when magnesium is heated with oxygen, then magnesium oxide is formed. In this reaction, two reactants, namely magnesium and oxygen, reacts to form one product called magnesium oxide. So, this reaction is an example of a combination reaction.

2. Decomposition Reaction

The reaction in which a compound splits up into two or more simpler substances are known as decomposition reactions. The decomposition reactions are carried out by applying heat, light, or electricity. Energy is provided by heat, light, or electricity, which breaks a compound down into two or more simpler compounds. Please keep in mind that a decomposition reaction is the inverse of a combination reaction. When a decomposition reaction is carried out by heating, it is called thermal decomposition.

For example, when calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide. So, this reaction is an example of a decomposition reaction.

3. Displacement Reaction

The reaction in which one element takes the place of another element in a compound is known as displacement reaction. In general, a more reactive element displaces a less reactive element from its compound.

For example, when a piece of iron (such as a nail) is immersed in a copper sulphate solution, then iron sulphate solution and copper metal are formed.

In this reaction, iron displaces copper from copper sulphate solution.  The deep blue colour of copper sulphate solution fades as a result of the formation of light green iron sulphate solution. A red-brown coating of copper metal is formed on the surface of iron metal. This displacement reaction occurs because iron is more reactive than copper.

4. Double Displacement Reaction

Double displacement reactions are those in which two compounds react by exchanging ions to form two new compounds. A double displacement reaction usually occurs in solution, and one of the insoluble products precipitates out.

For example, when silver nitrate solution is mixed with sodium chloride solution, a white precipitate of silver chloride forms along with sodium nitrate solution.

In this double displacement reaction, two compounds, silver nitrate and sodium chloride react to form two new compounds, silver chloride and sodium nitrate. An exchange of ions takes place in this reaction. Hence, this reaction is an example of a double displacement reaction.

5. Oxidation and Reduction Reactions

The addition or removal of oxygen or hydrogen elements is the basis for the earlier concept of oxidation and reduction. Thus, oxidation and reduction reactions can be defined in terms of oxygen or hydrogen as follows.

Oxidation:

i. The addition of oxygen to a substance is called oxidation.
ii. The removal of hydrogen from a substance is also called oxidation.

Reduction:

(i) The addition of hydrogen to a substance is called reduction. 
(ii) The removal of oxygen from a substance is also called reduction.

The oxidation and reduction reactions are also called redox reactions.

Effects of Oxidation in Everyday Life

Metals and food are both harmed by oxidation. The damaging effect of oxidation on metals is known as corrosion, and the effect on food is known as rancidity. Thus, there are two common effects of oxidation reactions that we see in everyday life. These are:

1. Metal corrosion
2. Food rancidity

1. Corrosion: Corrosion is the gradual deterioration of metals caused by the action of air, moisture, or a chemical (such as an acid) on their surface. Corrosion is primarily caused by the oxidation of metals by oxygen in the air. The most common type of corrosion is rusting of iron metal.

2. Rancidity: Rancidity is caused by the aerial oxidation of fats and oils in foods that result in an unpleasant odour and taste. Rancidity spoils the food materials prepared in fats and oils, which have been kept for a considerable time and makes them unfit for eating.

The following methods can be used to prevent the development of rancidity in food:

Important Questions on Chemical Reactions and Equations

Q.1. What is redox reaction?
Ans: Redox is a type of chemical reaction in which the oxidation states of atoms are changed.

Q.2. Give three types of decomposition reactions.
Ans: The three types of decomposition reactions are
1. Thermal decomposition reaction
2. Electrolytic decomposition reaction
3. Photo decomposition reaction

Q.3. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of chemical reaction?
Ans: It is a double displacement reaction. The chemical reaction involved is:

Summary

Chemical reactions are the process in which new substances with new properties are formed. Chemical reactions involve chemical change. During a chemical reaction, atoms of one element do not change into those of another element. The characteristics of chemical reactions are the evolution of gas, formation of a precipitate, change in temperature, colour, and change in taste. A chemical equation represents a chemical reaction using symbols and formulas of the substances involved.

PRACTICE QUESTIONS RELATED TO CHEMICAL REACTIONS

FAQs

Q.1. What are the types of chemical reactions?
Ans: The types of chemical reactions are
1. Combination reaction
2. Decomposition reaction
3. Displacement reaction
4. Double displacement reaction
5. Reduction and oxidation reaction

Q.2. What is the difference between chemical reaction and chemical equation?
Ans: Chemical reactions are the process in which new substances with new properties are formed. In comparison, a chemical equation represents a chemical reaction using symbols and formulae of the substances involved.

Q.3. What are chemical reactions examples?
Ans: Examples of chemical reactions are as follows;
Burning of magnesium ribbon in air.
\(2 \mathrm{Mg}+\mathrm{O}_{2} \rightarrow 2 \mathrm{MgO}\)
Formation of water
\(2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\)
Reaction of calcium hydroxide with carbon dioxide.
\({\rm{Ca}}{\left( {{\rm{OH}}} \right)_{2\left( {{\rm{aq}}} \right)}} + {\rm{C}}{{\rm{O}}_{2\left( {\rm{g}} \right)}} \to {\rm{CaC}}{{\rm{O}}_{3\left( {\rm{s}} \right)}} + {{\rm{H}}_2}{{\rm{O}}_{\left( {\rm{l}} \right)}}\)

Q.4. What is chemical equation and example?
Ans: A chemical equation represents a chemical reaction using symbols and formulae of the substances involved.
For example,
Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This reaction can be written as,
\(\text {Zinc} + \text {Sulphuric acid} \rightarrow \text {Zinc sulphate} + \text {Hydrogen gas}\)

Q.5. What is the importance of chemical equation?
Ans: Importance of chemical reactions are as follows:
A. A chemical reaction is represented using a chemical equation, which makes it simple to understand.
B. A chemical equation can accurately predict the amount of reactants required to prepare a product.
C. It is simple to determine the effect of temperature, pressure, and other variables on the state of the reaction.

Q.6. Explain the basic concepts of chemical reactions.
Ans: The basic concepts of chemical reactions are as follows:
1. A chemical reaction is a process by which two or more molecules interact to produce a new product \(\left( {\rm{s}} \right)\).
2. Compounds that interact to form new compounds are referred to as reactants, while the newly formed compounds are referred to as products.
3. A chemical change must occur in a chemical reaction, which is commonly observed with physical changes such as precipitation, heat production, colour change, and so on.
4. The rate of reaction is affected by factors such as pressure, temperature, and reactant concentration.
5. A reaction can occur between two atoms, ions, or molecules in which they form a new bond without destroying or creating an atom, but a new product is formed from reactants.

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