Chemical Reactions

What is a Chemical Reaction?

A chemical reaction is described as in which the bonds are broken within reactant molecules, and new bonds are formed within the product molecules to form the new substance.

Generally, there are chemical reactions all around us, from the metabolism of the food in our body to how the light that we get from the Sun is the result of chemical reactions. It is most important to know about the physical and chemical changes that take place either chemically or in our daily lives.


Description

Chemical reactions are said to be an integral part of technology, culture, and indeed of life itself. Smelting iron, burning fuels, making pottery & glass, brewing beer, and making cheese and wine are among several examples of the activities incorporating the chemical reactions, which have been known and used for the past thousands of years. Chemical reactions abound in the atmosphere and oceans, the geology of Earth, and in a vast array of the complicated processes that take place in all living systems.

Chemical reactions should be differentiated from physical changes. Physical changes include the changes of state, such as water evaporating to vapor and ice melting into water. If a physical change takes place, the physical properties of the substance will change, but its chemical identity will remain the same. No matter what its physical state, water (H2O) is given as the same compound, with every molecule composed of two atoms of hydrogen and one atom of oxygen.

However, if water, either as liquid, ice, or vapor, encounters the sodium metal (Na), the atoms will be redistributed to form the new substances sodium hydroxide (NaOH) and molecular hydrogen (H2). By this, we can know that a reaction or chemical change has taken place.


Example of a Chemical Reaction

A burning candle is given as the best example of both physical and chemical change. Simply take a candle and light it. As time passes, we can notice that the candle changes to wax. On the other hand, if you cover the candle with a jar, it will extinguish.


[Image will be uploaded soon]


In the above-given demonstration, the burning of a candle is defined as a chemical change, while the conversion of the candle to wax is a physical change. Whereas, in a physical change, there is basically a change of state of the substance. But, in the case of a chemical change, mostly a new substance is formed, where either energy is either given off or absorbed. Therefore, we can conclude that chemical changes are accompanied by certain physical changes.


Basic Concepts of Chemical Reactions

  • A Chemical Reaction is defined as a process that takes place when either two or more molecules interact to produce a new product (s).

  • Compounds, which interact to produce new compounds, are known as reactants, whereas the newly formed compounds are known as products.

  • Chemical reactions play an integral role in various industry verticals, customs, and even in our daily lives. They are continuously happening in our surroundings; for example, pottery, rusting of iron, fermentation of wine and more.

  • In a chemical reaction, a chemical change should take place, which is generally noticed with physical changes like heat production, precipitation, color change and so on.

  • A reaction can occur between either two ions or atoms or molecules, and they form a new bond, and no atom is either created or destroyed, but a new product is formed from reactants.

  • The rate of reaction completely depends on and is affected by factors like temperature, pressure, the concentration of reactants.


Chemical Equations

Due to the excess amounts of chemical reactions happening around us, a nomenclature was developed to simplify how we express the chemical reaction in a chemical equation form. A chemical equation is nothing but a mathematical statement that symbolizes the product formation from reactants while stating certain conditions for which the reaction has been conducted.

The reactants lie on the left-hand side, whereas the products formed on the right-hand side are connected either by one-headed or two-headed arrows. For example, a reaction is given below:

A + B → C + D

Here, both A and B are the reactants that react to form the products C and D. In an actual chemical equation; reactants can be denoted with the help of their chemical formula. To assure the law of conservation of mass, a chemical equation should be balanced. The number of atoms present on both sides must be equal. This is said to be equation balancing.

Let us consider an actual chemical reaction between Oxygen (O2) and Methane(CH4), which can be shown as:


[Image will be uploaded soon]


Here we can observe how the number of every atom on the left side is balanced on the right side, which is stated by the law of conservation of mass.


Types of Chemical Reactions

Let us discuss the types of chemical reactions in detail with examples.

The basis for various types of reactions is given as the product formed, the changes that take place, the reactants involved, and so on. Some types of reactions are given below:

  1. Combustion reaction

  2. Decomposition reaction

  3. Neutralization reaction

  4. Redox Reaction

  5. Precipitation or Double-Displacement Reaction

  6. Synthesis reaction

1. Combustion Reaction

A combustion reaction is defined as a reaction having a combustible material with an oxidizer to form an oxidized product. An oxidizer is given as a chemical fuel that requires burning, generally oxygen. Consider the example of the combustion of magnesium metal as given below.

2Mg + O2 → 2MgO + Heat

Here, 2 magnesium atoms get to react with a molecule of oxygen-producing 2 molecules of the compound magnesium oxide-releasing some heat in the process.


2. Decomposition Reaction

A Decomposition reaction is defined as a reaction where a single component breaks down into multiple products. Certain energy changes in the environment have to be made like light, heat, or electricity breaking bonds of the compound. Consider an example of the decomposition of calcium carbonate forming CaO (Quick Lime), which is a primary component of cement, as given below:

CaCO3(s) → Heat CaO(s) + CO2(g)


[Image will be uploaded soon]


Here, the compound Calcium carbonate, when heated, breaks down into Carbon Dioxide and Calcium Oxide.


3. Neutralization Reaction

A Neutralization reaction is basically defined as the reaction between an acid and a base by forming salt and water as the products. The water molecule that is formed is by the combination of H+ ions and OH ions. The entire pH of the products when a strong acid and base undergo a neutralization reaction will be 7. Consider an example of the neutralization reaction between Sodium Hydroxide and Hydrochloric acid giving out sodium chloride (called Common Salt) and water.

HCl + NaOH → NaCl + H2O

Here, the Hydrochloric acid and Sodium Hydroxide (an acid and a base) react in a neutralization reaction to form Sodium Chloride (called Common Salt) and water as the products.


4. Redox Reaction

A REDuction-OXidation reaction is defined as a reaction where there is a transfer of electrons between the chemical species. Let us consider an example of an electrochemical cell-like redox reaction between Hydrogen and Zinc, which is chemically shown as follows:

Zn + 2H+ → Zn2+ + H2

Here, a Zinc atom reacts with 2 ions of the positively charged hydrogen, where the electrons get transferred from the zinc atom and hydrogen becomes a stable molecule and Zinc ion is the resultant product.


5. Double-Displacement or Precipitation Reaction

This is a type of displacement reaction (which is the precipitation reaction), where two compounds react, and consequently, their cations and anions switch places, forming two new products. Consider an example of the reaction between sodium chloride and silver nitrate. The products will be sodium nitrate and silver chloride after the double-displacement reaction, which is shown below:

AgNO3 + NaCl → AgCl + NaNO3


[Image will be uploaded soon]


Here, Sodium Chloride and Silver Nitrate undergo a double displacement reaction. Wherein Silver replaces the Sodium in Sodium Chloride and Sodium joins with Nitrate becoming Sodium Nitrate along with the Silver Chloride as the resultant product.


6. Synthesis Reaction

A Synthesis reaction is the most basic type of reaction wherein various simple compounds combine under certain physical conditions resulting in a complex product. Here, always, the product will be a compound. Let us consider the Synthesis reaction of sodium chloride with reactants chloride gas and solid sodium, as shown below:

2Na(s) + Cl(g) → 2NaCl(s)

Here, there are 2 Atoms of solid Sodium reacting with Chlorine gas forming in Sodium Chloride viz. Common Salt as the product.


Important Points to Remember

  • A physical change, such as a state dissolving or change, does not create any new substances, but a chemical change does.

  • In a chemical reaction, both the molecules and atoms, which interact with each other, are known as reactants.

  • In a chemical reaction, both the molecules and atoms produced by the reaction are referred to as products.

  • Only the atoms accessible in the reactants can end up in the products in a chemical reaction. No new atoms are either created or destroyed.

  • In a chemical reaction, reactants usually contact each other, bonds between atoms in the reactants are broken, and the atoms rearrange and form new bonds to form the products.

  • In a chemical change, a new compound can be formed. Whereas, in a physical change, the substance changes its existence state.

  • Ions or atoms, or molecules that react to form a new substance, are known as reactants; the new molecules or atoms formed are called products.

  • A chemical reaction is the one that always follows the law of conservation of mass. It means, no atom is either created or destroyed, but only a new product is formed from reactants.

FAQs (Frequently Asked Questions)

1. Give the Synthesis of Chemical Reactions?

Answer: When making a new substance from the other substances, chemists say that either they carry out a synthesis or synthesize the new material. Reactants are converted to products, and the process is symbolized by the chemical equation.


For example, sulfur (S) and iron (Fe) combine to form iron sulfide (FeS).

Fe(s) + S(s) → FeS(s)

2. What are the Decomposition Reactions?

Answer: In 1774, the scientist named “Joseph Priestley” turned his curiosity to the mineral known as cinnabar, which is a red brick mineral. When he exposed the mineral to sunlight magnified using a strong magnifying lens, he discovered a gas that he described as having a "exalted character" since a candle burned brightly in the gas (Priestley - in 1775).


Without realizing it, Priestley had discovered oxygen as a result of the decomposition reaction. Often, the decomposition reactions are thought of as the opposite of synthesis reactions since they involve a compound that is broken down either into simpler compounds or even elements. Priestley had used heat to break down mercury (II) oxide (also known as cinnabar) into its individual elements in the case of oxygen.

3. What are Combustion Reactions?

Answer: The controlled use of the fire was given as a crucial development for early civilization. While it is not easy to pin down the actual time that humans first tamed the combustion reactions, which produce fire, according to a recent study, it occurred at least a million years ago in a South African cave (in Berna et al. 2012).


Chemically, the combustion is no more than the reaction of Fuel (oil, wood, gasoline.) with oxygen. For combustion to occur, there must be oxygen and fuel gas. However, often, these reactions need activation energy, which can be provided either by a ‘spark’ or a source of energy for ignition. Oxygen, Fuel, and energy are the three things that makeup what is known as the fire triangle, and any one of them being absent means that combustion will not occur.

4. What are the Kinetic Considerations?

Answer: Commonly, chemical reactions require an initial input of energy to start the process. However, the combustion of paper, wood or methane is said to be an exothermic process, a burning match or a spark or is required to initiate this reaction. The energy that is supplied by a match arises from an exothermic chemical reaction, which is itself initiated by the frictional heat generated by rubbing the match on a suitable surface.


In a few reactions, the energy to initiate a reaction can be provided by the light. A number of reactions in Earth’s atmosphere are either photochemical or light-driven reactions, which are initiated by solar radiation. An example is given as transformation of ozone (O3) into oxygen (O2) in the troposphere. The absorption of Uv light from the Sun to initiate this reaction potentially prevents harmful high-energy radiation from reaching the surface of Earth.