Chemical Equations

A chemical equation is a common term of day to day chemistry. Chemical equations were first formulated in the year 1615 by a French chemist Jean Beguin. A chemical equation is nothing but a written representation, using numbers and symbols, of the process that occurs during a chemical reaction.

What is the Chemical Equation?

If we summarise this in chemistry language then: A chemical equation shows the starting compounds i.e., the reactants on the left-hand side and the final compounds i.e., the products on the right-hand side, separated by an arrow. The numbers of atoms of each element and the total charge in the balanced chemical equation are identical on both sides of the equation.

How to Write a Chemical Equation?

To write a chemical equation we should first understand its participants which are:-

  1. Elements that are represented by their symbols.

  2. Reactants also are known as Substrates are written on the left-hand side and are the reacting entities in the equation.

  3. Products are written on the right-hand side and are the output formed due to the chemical reaction taking place in the elements.

  4.  An Arrow which represents the direction in which the chemical equation flows. The symbol  ‘→’ is used to represent Arrow and is read as “gives rise to” or “yields.”

Example for Chemical Equation 

Photosynthesis is the process in plants and certain other organisms that uses the energy from the sun to convert carbon dioxide and water into glucose and oxygen.

Chemical Equation for Photosynthesis

6CO+ 6 H2O → C6H12O+ 6O2 

Where:
CO2 = carbon dioxide 
H2O = water
light is required
C6H12O6 = glucose
O2 = oxygen

The above chemical equation for photosynthesis describes how the chemical reaction of carbon dioxide, water and light energy produces carbohydrates and oxygen.

Coefficients assigned to each of the symbols indicate the stoichiometric numbers whereas subscripts indicate the number of atoms of an element present in a chemical species.

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Direction of Chemical Reaction

It is a convention that the arrow between the reactants and products should point from left to right. However, the following symbols are used as needed in an equation:

  • For a net forward reaction, the symbol ‘→’ is used.

  • For a state of chemical equilibrium, the symbol ‘⇌’ is used.

  • To denote stoichiometric relationships, the ‘=’ symbol is used.

  • For a reaction that occurs in both forward and backward directions, the symbol ‘⇄’ is used.

When multiple entities are used in a chemical equation, they are separated from each other with the symbol “+.”

Physical States of Reacting Entities

To describe the physical states of reacting entities during the course of reaction following symbols can be used :

  • The symbol (s) for solid-state

  • The symbol (l) denotes the liquid state

  • The symbol (g) implies a gaseous state.

  • The (aq) symbol denotes an aqueous solution.

 Also in some reactions, the ‘↓’ symbol is written next to the chemical formula of the reactant or product to describe them as precipitates.

What is a Combustion Reaction?

 A reaction in which a substance reacts with oxygen gas and releases energy in the form of light and heat is known as a combustion reaction. Combustion reactions must involve O2 as one reactant. The combustion reaction of hydrogen gas produces water vapor.

The combustion reaction of organic compounds normally is as follows :

organic compound + oxygen => water + carbon dioxide.

How to Balance a Redox Reaction

When elements in a chemical reaction gain or lose electrons, and this results in an increase or decrease in oxidation numbers, then it is termed as Oxidation-Reduction or “redox” reaction.

There are Two Methods for Balancing a Redox Reaction Namely:

  1. Oxidation Number Method :

It is based on the difference in oxidation number of oxidizing agent and the reducing agent.

  1. Half Equation/Reaction Method

In this method, the equation is split into two half-equations for oxidation and reduction.


FAQ (Frequently Asked Questions)

1. What is the Chemical Equation?

A chemical equation is a written representation, using numbers and symbols, of the process that occurs during a chemical reaction with reactants on the left-hand side and products on the right-hand side connected by an arrow.

2. What is a Chemical Equation for Photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2 

3. Describe the Positions of Reactants and Products.

Reactants are conventionally written on the left-hand side and products on the right-hand side.

4. State Various Symbols used to Describe the Direction of the Chemical Equation.

Following are the symbols:

  1. For the net forward reaction, the symbol ‘→’ is used.

  2. For a state of chemical equilibrium, the symbol ‘⇌’ is used.

  3. For stoichiometric relationships, the ‘=’ symbol is used.

  4. For a reaction in both forward and backward directions, the symbol ‘⇄’ is used.

5. What is a Redox Reaction? State its Two Methods

When elements in a chemical reaction gain or lose electrons, resulting in an increase or decrease in oxidation numbers, it is known as a redox reaction.

Two methods for balancing a redox reaction are: Oxidation number and half equation.

6. What is the Combustion Reaction?

A combustion reaction is an exothermic reaction in which something reacts with oxygen.