Chemical Equations

A chemical equation is a common term of day-to-day chemistry. Chemical equations were first formulated in the year 1615 by 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.

French chemist Jean Beguin formulated the chemical equation for the first time in 1615. Chemical equations in chemistry are used as symbolic representations of chemical reactions in which the reactants and the products are written in terms of their respective chemical formulae. The chemical equations also consist of symbols that represent factors such as the direction of the reaction and the physical states of the reacting entities. Chemical equations are an easy way to represent chemical reactions on paper.

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 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 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.”

5. In a chemical equation, coefficients are also assigned to each of the symbols of their corresponding reactants and products.  The coefficients of entities are the exact value of the stoichiometric number or that entity in chemical equations. 

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

6CO2 + 6 H2O → C6H12O6 + 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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What are Chemical Reactions?

Chemical reactions can be described as a process in which one or more substances called reactants are converted into one or more substances known as the products. The substances, here, are either compounds or chemical elements. In simple words, when there is a rearrangement in constituent atoms of the reactants to create different substances as products, it can be said that a chemical reaction has occurred.

These reactions are an important and integral part of technology and life on Earth. Some of the common examples of chemical reactions that we witness every day are burning fuels, smelting of iron, making glass and pottery, brewing beer, and making wine and cheese.

Importance of Chemical Reactions

The existence of living organisms is possible on Earth because of the chemical reactions. Here are a few reasons the existence of chemical reactions is important to us:

• Chemical reactions are required to understand the properties of the matter. These reactions help us to learn and understand the chemical properties when a sample interacts with a matter. These chemical properties can lead to the discovery of unknown specimens and explain how different types of matter react with each other.

• By studying and observing the chemical reaction, it is possible to derive the working of the natural world. It is the very chemical reaction that turns food into fuel in the human body, makes fireworks explode, changes the form of food when it is cooked and makes soap removes dirt and oil.

• The most important and beneficial discovery made by humans – fire is also a product of simple chemical reactions.

• To study outer space and other planets scientists take the help of chemical reactions. Owing to these chemical reactions we can even determine the sustainability of other planets and moons.

The 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 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.

2. Half Equation/Reaction Method

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

Representation of Input of Energy in a Chemical Equation 

In some cases, the input of energy needs to be represented in chemical equations to proceed with the experiment. These requirements of energy of such reactions are represented in their corresponding chemical equations with the help of some symbols mentioned below:

• Delta is a Greek letter that is used in its upper-case form to state that input of heat energy is required by the reaction. 

• Another symbol used is the formula written as ‘hv’ that describes the energy of a photon. It is used above the arrow symbol in a chemical reaction as a statement that the reaction requires an input of light to proceed.

One must notice that the coefficients which are assigned to each entity are used such in a chemical equation that the entire equation obeys the law of conservation of charge and the law of conservation of mass.

Ionic Equation 

Ionic chemical equations are slightly different from that of a classic case of chemical equations. Ionic chemicals involve electrolytes which are substances that dissociate into ions when dissolved in polar solvents. These electrolytes are split up and written as individual ions when written in ionic chemical equations.

These types of equations are very useful while explaining single replacement reactions and salt metathesis reactions, commonly known as double displacement reactions.