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Chapter 15 – Chemical reactions

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

You must have noticed the difference in the taste of milk and curd or the difference between an old iron plate/rod and a brand new one. If you look for the difference in substances made from the same constituents, you might wonder how milk can look entirely different from curd, although both are made from milk. A direct and straightforward explanation for this is, almost every substance around us changes its chemical properties due to the influence of other substances or external properties such as temperature, pressure, and humidity. Scientifically, whenever reactants (metal or nonmetal, element or molecule) react with one another to produce a component (product) that may or may not have the reactants’ properties is known as a chemical reaction.

For example: HCl + NaOH  NaCl + H20

Millions of changes occur around us. How to determine if it is a chemical reaction or not? Following are a few properties of a chemical reaction that might determine its identity:

  1. Change in the state of products after the reaction.
  2. Change in the color of the end product in comparison to the reactants.
  3. Evolution of gas or effervescence during the reaction
  4. Change in temperature before and after the reaction depending on whether the reaction is exothermic (releases heat at the end) or endothermic (uses heat to complete the reaction).

Any kind of chemical reaction such as exothermic or endothermic; produces precipitate or gaseous product or otherwise needs to be presented hat is a simple and easy-to-understand form. Mentioning a chemical reaction using words is lengthy and tiresome; hence the scientific community uses chemical equations to resolve it.

For example Zinc + Sulphuric acid Zinc sulfate + Hydrogen

Chemical Equation with symbols: Zn + H2SO4  ZNSO4 + H2O

The difference between both is that the above reaction is lengthy and doesn’t explain how the reaction occurs. On the other hand, the second reaction is simple, self-explanatory, and brief.

Everything surrounding us is constantly changing, some gradually and some drastically. Microscopically, it doesn’t necessarily mean atomic or subatomic particles are getting changed. For example, plants and trees perform photosynthesis; they use CO2 and H2O to produce glucose and oxygen. Another example is making tea; when tea leaves and water are combined and supplied heat, they react to produce tea. A chemical reaction uses its reactants to produce a product that was previously not present in the reaction. Sometimes the reactants combine, sometimes they displace, sometimes they neutralize one another, and so on. Let us look at the type of chemical reactions:

1. Combination reaction

The type of reaction where two or more reactants combine to form a single product is known as a combination reaction. In this reaction, the reactants (typically two or more) react with one another in favorable conditions to form a single product (having different chemical properties to its reactants).

For example:

  1. Combustion of Coal (pure): C (s)+ O2(g)   CO2(g)
    Here the Coal is (C) in a solid-state that reacts with gaseous Oxygen (O2) to give Carbon Dioxide (CO2)
  2. CaO(s) + H2O(l) → Ca(OH) 2 (aq)
    Here the Calcium Oxide (quick lime) reacts with water to produce Calcium Hydroxide (slaked lime).

2. Decomposition reaction

A chemical reaction with only one reactant that produces more than one product using external factors such as heat, light, or electricity is known as a decomposition reaction. It is opposite to the combination reaction where reactants are multiple, and the reaction can be exothermic.

For example:

CaCO3(s)  CaO(s) + CO2 (g)

Here the solid-state Calcium Carbonate (CaCO3) under the presence of heat produces Calcium Oxide (CaO) and carbon dioxide gas (CO2).

3. Displacement reaction

This is a type of chemical reaction in which the relatively high reactive metal reacts with the low reactive metal salt to displace the lower reactive metal from salt. Typically in any reaction, the metal with higher reactivity displaces the metal with lower reactivity. This reaction is widely used in electroplating techniques.

For example:

Fe(s) + CuSO4 (aq) → FeSO4(aq) + Cu(s)

In this reaction, Iron (Fe) metal, which is highly reactive, reacts with Copper Sulphate salt (CuSO4) to displace Copper and form Ferrous Sulphate salt (FeSO4).

4. Double displacement reaction

This is also known as the precipitation reaction. A precipitation reaction is when the end product of the reaction is a residue. Reactions in which an exchange of ions occurs between reactants to produce two new products with displaced ions are double displacement reactions.

For example:

Na2SO4 (aq) + BaCl2 (aq) → BaSO4(s) + 2NaCl (aq)

In this reaction, aqueous reactants Sodium Sulphate (Na2SO4) reacts with Barium Chloride (BaCl2) to produce Barium Sulphate (BaSO4) and Sodium Chloride (NaCl).

5. Oxidation and reduction

During a reaction, when a reactant gains oxygen, it is said to be oxidized, and the reactant that loses oxygen or gains hydrogen is known to be reduced. A redox reaction occurs when one reactant is oxidized, and one reactant is reduced to produce the final product.

For example:

  1.     ZnO + C → Zn +CO
  2.     MnO2 + HCl MnCl2 + H2O + Cl2

In both the above reactions, Zinc oxide (ZnO) and Manganese Oxide (MnO2) are being reduced, whereas Carbon (C) and Hydrochloric Acid (HCl) are being oxidized.

1. What are the four types of chemical reactions?

Answer: 4 types of chemical reactions are

  •       Lewis acid-base reactions
  •       Proton transfer reactions
  •       Electron transfer reactions
  •       Radical reactions

2. What is a chemical reaction example?

Answer: Some everyday examples of chemical reactions are respiration, photosynthesis, combustion of fuel, rusting of metal, etc. Combustion of methane is CH4 + O2 C02 + H2O

3. What are the six chemical reactions?

Answer: 6 types of chemical reactions are

  •       Combination reaction
  •       Decomposition reaction
  •       Displacement reaction
  •       Neutralization or Double displacement reaction
  •       Precipitation reaction
  •       Combustion reaction

4. Can a chemical reaction be reversed?

Answer: Few chemical reactions can be reversed. Most of the reversible chemical reactions are expensive and difficult to achieve.

5. What is the biggest chemical reaction?

Answer: The most important chemical reaction occurring in our environment is respiration and photosynthesis.

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