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Chemical Equations – Definition, Representation, Types

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  • Last Updated : 20 Nov, 2021

Chemical reactions are the processes that result in the formation of new substances with new properties. Chemical reactions cause changes in the environment. A rearrangement of atoms occurs between the reacting components during chemical reactions, resulting in the formation of new compounds with fundamentally different properties. Chemical reactions involve the breaking of odd chemical bonds between reacting substance atoms, followed by the formation of new chemical bonds between the rearranged atoms of new substances. Atoms of one element do not transform into those of another during a chemical reaction. A chemical reaction is nothing more than an atom rearrangement.

What are Chemical Equations?

Chemical equations are symbolic representations of chemical reactions that express the reactants and products in terms of their chemical formulae. Symbols are also used to denote elements like the reaction’s direction and the physical states of the reacting entities. Jean Beguin, a French chemist, was the first to formulate chemical equations in 1615.

Chemical formulas and other symbols are used to represent the initial elements, or reactants, which are written on the left side of the equation by convention, and the final compounds, or products, which are written on the right side of the equation by convention. From the reactant to the products is indicated by an arrow. “Yields” or “reacts to form” is just how the arrow is read.

This example shows the basic elements of any chemical equation:

                                                  CH4       +         2O2        →       CO2           +         2H2O

  • Reactants are the chemicals that undergo reaction, and their formulas are found on the left side of the equation.
  • The substances formed by the reaction are referred to as products, and their formulas are written on the right side of the equation.
  • Individual reactant and product formulations are separated by plus signs (+), and the reactant and product (left and right) sides of the equation are separated by an arrow (→).
  • Coefficients (numbers placed immediately to the left of each formula) represent the relative numbers of reactant and product species.

Short-Hand Method of Representing a Chemical Reaction.

A chemical equation is a means of describing a chemical reaction using symbols and equations for the substances involved in the process. The example below demonstrates how to clearly understand the meaning of a chemical equation.

Zinc sulphate and hydrogen gas are formed when zinc metal combines with dilute sulphuric acid. This reaction can be expressed in words as follows:

Zinc    +      Sulphuric acid      →         Zinc sulphate    +     Hydrogen

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

  • The symbol of zinc is Zn.
  • The formula of sulphuric acid is H2SO4.
  • ZnSO4 is the formula of zinc sulphate.
  • H2 is the formula of hydrogen.

We derive the following chemical equation by placing the symbols and formulas of all the chemicals in the above word equation.

Zn   +      H2SO4           →         ZnSO4    +    H2
Reactants                                      Products

  • Reactants are compounds that mix or react together. Zinc and sulphuric acid are the reactants in the above reaction. In an equation, the reactants are always written on the left side with a plus sign (+) between them.
  • Products are the new substances produced during a reaction. The products of the reaction are zinc sulphate and hydrogen. In an equation, the products are always written on the right side, with a plus symbol (+) between them.
  • Between the reactants and the products, an arrow sign (→) pointing to the right is placed. This arrow indicates that the substances on the left-hand side of the equation are combined to produce the substances on the right-hand side. It should be obvious by now that the chemical equation is a shorthand method of representing a chemical reaction.

Balanced Chemical Equation

In a balanced chemical equation, the reactants and products have an equal number of atoms of different elements. In other words, on both sides of a balanced chemical equation, the number of atoms of the various elements is equal. The following example will help to clarify this point.

Zinc sulphate and hydrogen are formed when zinc combines with dilute sulfuric acid. This can be written as an equation:

Zn          +       H2SO4      →       ZnSO2          +          H2 

In the following table, let’s count how many atoms each element has in the reactants and products individually.

Number of atoms of elements

In reactants

In products

Zn

1

1

H

2

2

S

1

1

O

4

4

We found that the reactants and products both contain one zinc atom. Two hydrogen atoms are found in reactants and two hydrogen atoms are found in products. Reactants and products each have one sulphur atom in them. Finally, the reactants have four oxygen atoms, and the product has four oxygen atoms as well. As a result, the reactants and products have an equal number of atoms of different elements, making the above-mentioned chemical equation balanced. A balanced chemical equation contains equal masses of various elements in reactants and products because the number of atoms of various elements in reactants and products is equal.

Unbalanced Chemical Equation

The reactants and products in an unbalanced chemical equation have an uneven number of atoms of one or more elements. An unbalanced chemical equation, in other words, has an uneven number of atoms of one or more elements on both sides. The following example will help to clarify this point.

Water is formed when hydrogen combines with oxygen. This reaction can be expressed by the equation as.

H2             +          O2         →             H2O

In the following table, let’s count how many hydrogen and oxygen atoms there are in the reactants and products.

Number of atoms of elements

In reactants

In products

H

2

2

O

2

1

In this equation, the reactants have two hydrogen atoms, and the products have two hydrogen atoms as well. However, the reactants and products have different numbers of oxygen atoms. The reactants, on the left side, have two oxygen atoms, but the products, on the right side, have just one. The preceding chemical equation is unbalanced because the number of oxygen atoms in the reactants and products is uneven. Due to the uneven number of atoms of various elements in reactants and products, it can be said that an imbalanced equation is one in which the masses of various elements in the reactants and products are uneven.

Sample Questions

Question 1: What distinguishes chemical reactions from other types of reactions?

Answer:

Chemical reactions have a number of essential features.

  1. A gas’s evolution.
  2. Precipitation is the formation of a substance.
  3. A colour change takes place.
  4. The temperature change.
  5. The state change.

Question 2: Why should chemical equations be balanced?

Answer:

To satisfy the law of mass conservation in chemical reactions, the chemical equations must be balanced.

Question 3. Is the following equation balanced or unbalanced?

CH4          +       O2     →          CO2        +              H2O

Answer:

In a balanced chemical equation, the reactants and products have an equal number of atoms of different elements.

The reactants and products in an unbalanced chemical equation have an uneven number of atoms of one or more elements.

There is 1 atom of carbon atom in the reactants as well as in the products. There are 4 atoms of hydrogen in the reactants but there are 2 atoms of hydrogen in the products. Also, there are 2 atoms of oxygen in the reactants but there are 3 atoms of oxygen in the products. Since there is an uneven number of atoms of hydrogen and oxygen in the reactants and products. Hence the above reaction is unbalanced.

Question 4: A chemical reaction is balanced on what basis?

Answer:

A chemical reaction is said to be balanced if the reactants and products have an equal number of atoms of different elements.

Question 5. What is the law of mass conservation?

Answer:

The law of conservation of mass states that matter cannot be generated or destroyed in a chemical reaction, and as a result, in a chemical reaction, the number of atoms of various elements in reactants and products must be equal.


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