What is Chemical Reaction in Chemistry | Types, eg

Definition of Chemical Reaction

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

Summary

chemical reactions in chemistry

Chemical reaction, a process in which one or more substances or reactants are converted to one or more different substances or products. Substances are either chemical elements or compounds.

A chemical reaction rearranges the constituent atoms of the reactants to create different substances as
products. Chemical reactions are an integral part of technology, of culture, and indeed of life itself.

Burning fuels, melting iron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions. That have been known and used for
thousands of years.

Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.

Chemical reactions are all around us, from the metabolism of food in our body to how the light we get from the sun is the results of chemical reactions. Before beginning with chemical reactions, it is important to know about physical and chemical changes.

Chemical reactions happen absolutely everywhere. While we sometimes associate chemical reactions with the sterile environment of the test tube and the laboratory – nothing could be further from the truth. In fact, the colossal number of transformations make for a dizzying, almost incompre hensible array of new
substances and energy changes that take place in our world every second of every day.

In nature, chemical reactions can be much less controlled than you’ll find in the lab, sometimes far messier, and they generally occur whether you want them to or not. Whether it be a fire raging across a forest.

The slow process of iron rusting in the presence of oxygen and water over a period of years, or the delicate way in which fruit ripens on a tree. The process of converting one set of chemical substances (the reactants) to another set of substances (the products) is one known as a chemical reaction.

Though chemical reactions have been occurring on Earth since the beginning of time, it wasn’t until the 18th century that the early chemists started to understand them. Processes like fermentation, in which sugars are chemically converted into alcohol, have been known for centuries.

However, the chemical basis of the reaction was not understood. What were these transformations and how were they controlled? These questions could only be answered when the transition from alchemy to
chemistry as a quantitative and experimental science took place.

More About Chemical Reaction

  • A Chemical Reaction is a process that occurs when two or more molecules interact to form a new product(s).
  • Compounds that interact to produce new compounds are called reactants whereas the newly formed compounds are called products.
  • Chemical reactions play an integral role in different industries, customs and even in our daily life. They are continuously happening in our general surroundings; for example, rusting of iron, pottery, fermentation of wine and so on.
  • In a chemical reaction, a chemical change must occur. Which is generally observed with physical changes like precipitation, heat production, color change etc.
  • A reaction can take place between two atoms or ions or molecules. And they form a new bond and no atom is destroyed or created. But a new product is formed from reactants.
  • The rate of reaction depends on and is affected by factors like pressure, temperature, the concentration of reactants.

History of Chemical Reaction

Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity. Initial theories of transformation of materials were developed by Greek philosophers. Such as the Four-Element Theory of Empedocles stating that any substance is composed of the four basic elements – fire, water, air and earth.

In the Middle Ages, chemical transformations were studied by alchemists. They attempted, in particular, to convert lead into gold. For which purpose they used reactions of lead and lead-copper alloys with sulfur.,

The artificial production of chemical substances already was a central goal for medieval alchemists. Examples include the syn thesis ofammonium chloride from organic substances as described in the works (c. 850–950) attributed to Jabir ibn Haiyan, or the production of mineral acids such as sulfuric and nitric acids by later alchemists, starting from c. 1300.

The production of mineral acids involved the heating of sulfate and nitrate minerals such as copper sulfate, alum and saltpeter. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid and sodium chloride.

With the development of the lead chamber process in 1746 and the Leblanc process, allowing large -scale production of sulfuric acid and sodium carbonate, respectively, chemical reactions became implemented into the industry.

Further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis.

From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, and Isaac Newton tried to establish theories of the experimentally observed chemical transformations.

The phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of a fire-like element called “phlogiston”. Which was contained within combustible bodies and released during combustion. This proved to be false in 1785 by Antoine Lavoisier who found the correct explanation of the combustion as reaction with oxygen from the air. Joseph Louis Gay-Lussac recognized in 1808 that gases always react in a certain relationship with each other.

Based on this idea and the atomic theory of John Dalton, Joseph Proust had developed the law of definite proportions. Which later resulted in the concepts of stoichiometry and chemical equations.

Types of Chemical Reactions

The basis for different types of reactions is the product formed, the changes that occur, the reactants involved and so on.

Different types of reactions are

  • Combustion Reaction
  • Decomposition Reaction
  • Neutralization Reaction
  • Redox Reaction
  • Precipitation or Double-Displacement Reaction
  • Synthesis Reaction

Combustion Reaction

cumbustion reaction in chemistry

A combustion reaction is a reaction with a combustible material with an oxidizer to give an oxidized product. An oxidizer is a chemical a fuel requires to burn, generally oxygen. Consider the example of combustion of magnesium metal.

2Mg + O2 →2MgO + Heat

Here, 2 Magnesium atoms react with a molecule of Oxygen. Producing 2 molecules of the compound magnesium oxide releasing some heat in the process.

Decomposition Reaction

decomposition reactions

A Decomposition reaction is a reaction in which a single component breaks down into multiple products. Certain changes in energy in the environment have to be made like heat, light or electricity breaking bonds of the compound.

Consider the example of the decomposition of calcium carbonate giving out CaO (Quick Lime). Which is a major component of cement.

CaCO3 (s) → CaO(s) + CO2 (g)

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

Neutralization Reaction

neutralization reactions

A Neutralization reaction is basically the reaction between an acid and a base giving salt and water as the products. The water molecule formed is by the combination of OH ions and H+ ions. The overall pH of the products when a strong acid and a strong base undergo a neutralization reaction will be 7.

Consider the example of the neutralization reaction between Hydrochloric acid and Sodium Hydroxide giving out sodium chloride(Common Salt) and water.

HCl + NaOH → NaCl + H2O

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

Redox Reaction

redox reactions

A Reduction-Oxidation reaction is a reaction in which there is a transfer of electrons between chemical species.

Let us consider the example of an electrochemical cell-like redox reaction between Zinc and Hydrogen.

Zn + 2H+ →Zn2+ + H2

Here, A Zinc atom reacts with 2 ions of positively charged hydrogen to which electrons get transferred from Zinc atom and Hydrogen becomes a stable molecule and Zinc ion is the product.

Precipitation or Double-Displacement Reaction

double dispacement reactions

It is a type of displacement reaction in which two compounds react and consequently. Their anions and cations switch places forming two new products.

Consider the example of the reaction between silver nitrate and sodium chloride. The products will be silver chloride and sodium nitrate after the doubledisplacement reaction.

AgNO3 + NaCl → AgCl + NaNO3

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

Synthesis Chemical Reaction

synthesis reaction

A Synthesis reaction is one of the most basic types of reaction wherein multiple simple compounds combine under certain physical conditions giving out a complex product. The product will always be a compound.

Let us consider the Synthesis reaction of sodium chloride with reactants solid sodium and chloride gas.

2Na(s) + Cl(g) → 2NaCl(s)

Here, we have 2 Atoms of solid Sodium reacting with Chlorine gas giving out Sodium Chloride viz. Common Salt as the product.

Chemical Equation

chemical equation

Chemical equations are symbolic representations of chemical reactions. In which the reactants and the products are expressed in terms of their respective chemical formula. They also make use of symbols to represent factors such as the direction of the reaction and the physical states of the
reacting entities.

Chemical equations were first formulated by the French chemist Jean Beguin in the year 1615. Due to the vast amounts of chemical reactions happening around us, a nomenclature was developed to simplify how we express a chemical reaction in the form of a chemical equation.

A chemical equation is nothing but a mathematical statement which symbolizes the product formation from
reactants while stating certain condition for which how the reaction has been conducted.

The reactants are on the left-hand side whereas products formed on the right-hand side connected by a one-headed or two-headed arrows.

For example, a reaction

A + B → C + D

Here, A and B are the reactants, which react to form the products C and D. In an actual chemical equation, reactants are den oted by their chemical formula.

In order to assure the law of conservation of mass, a chemical equation must be balanced i.e. the number of atoms on both sides must be equal.

This is the balancing of the equation. Chemical reactions can be represented on paper with the help of chemical equations, an example for which is represented below (for the reaction between hydrogen gas and oxygen gas to form water).

2H2 + O2 → 2H2O

It can be observed in the example provided above that the reacting entities are written on the left-hand side. Whereas the products that are formed from the chemical reactions are written on the right-hand side of the chemical equation.

Representing the Direction of the Chemical Reaction

The reactants and the products (for which the chemical formulae are written in chemical equations) can be separated by one of the following four symbols

  • In order to describe a net forward reaction, the symbol ‘→’ is used.
  • In order to describe a state of chemical equilibrium, the symbol ‘⇌’ is used.
  • To denote stoichiometric relationships, the ‘=’ symbol is used.
  • In order to describe a reaction that occurs in both forward and backward directions, the symbol ‘⇄’ is used.

Multiple entities on either side of the reaction symbols describe above are separated from each other with the help of the ‘+ ’ symbol in a chemical equation. It can be noted that the ‘→’ symbol, when used in a chemical equation, is often read as ‘gives rise to’ or ‘yields’.

Anatomy of A Chemical Equation

Chemical equations are always linked to chemical reactions. Since they are the shorthand by which chemical reactions are described. That fact alone makes equations incredibly important. But equations also have a crucial role to play in describing the quantitative aspect of chemistry. Something that we formally call stoichiometry.

All chemical reactions take on the same, basic format. The starting substances, or reactants, are listed using their chemical formula to the left-hand side of an arrow, with multiple reactants separated with plus signs. In the case of a reaction between carbon and oxygen :

C + O2

To the right hand of the arrow one finds the chemical formulas of the new substance or substances (known as the products) tha t are produced by the chemical reaction. In this case, since carbon dioxide is the result of burning carbon in the presence of oxygen:

[Reactants] C + O2 → CO2 [Products]

Since reactions can result in both physical as well as chemical changes, each substance is given a state symbol written as a subscript to the right of the formula. This describes the physical form of the reactants and products.

Common state abbreviations are (s) for solids, (l) for liquid s, (g) for gases and (aq) for any aqueous
substances, i.e., those dissolved in water.

C(s) + O2(g) → CO2(g)

Finally, in order to ensure that this representation abides by the law of conservation of mass. The equation may need to be balanced by the addition of numbers in front of each species that create equal numbers of atoms of each element on each side of the equation.

In the case of the formation of carbon dioxide from carbon and oxygen. There is no need for the addition of such numbers (called the stoichiometric coefficients). Since 1 carbon atom and 2 oxygen atoms appear on each side of the equation.

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