What is Chemical Reaction?
A chemical reaction is a process in which reactants react chemically and convert into products by chemical transformation. For example, Respiration – we inhale oxygen which reacts with glucose and produces carbon dioxide, water and energy. The reaction is given below.
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
Characteristics of a Chemical Reaction
Chemical reactions show one or more than one of the following characteristics.
Evolution of gas
Change in colour
Change in temperature
Change in energy
Formation of precipitate
Change in state
Now understand these characteristics in detail.
Evolution of Gas – Some chemical reactions take place with the evolution of gas. For example, when zinc reacts with hydrochloric acid, hydrogen gas is evolved with the formation of zinc chloride.
Reaction - Zn + 2HCl → ZnCl2 + H2
Change in Colour – Some chemical reactions are accompanied by a change in colour. For example, when colourless lead nitrate reacts with potassium iodide, it forms a yellow precipitate of lead iodide and colourless potassium nitrate.
Reaction – Pb(NO3)2 + 2KI → PbI2 + 2KNO3
Colourless Colourless Yellow ppt colourless
Change in Temperature – Some chemical reactions are accompanied by a change in temperature. For example, some reactions are exothermic in nature, while some are endothermic.
Change in Energy – Chemical reactions often involve a change in energy. During a chemical reaction, energy can be evolved or be absorbed. For example, in combustion reactions, energy is released, such as the burning of a fuel.
Formation of Precipitate – Some chemical reactions are accompanied by the formation of the precipitate. For example, barium chloride reacts with sodium sulphate and forms sodium chloride and precipitate of barium sulfate.
Reaction – BaCl2 + Na2SO4 —> BaSO4 + NaCl
Precipitate
Change in State – Some chemical reactions are accompanied by a change in state. For example, ammonia gas reacts with hydrogen chloride gas and forms solid ammonium chloride crystals.
Reaction – NH3(g) + HCl(g) —-> NH4Cl(s)
Types of Chemical Reactions
Chemical reactions are of many types. Here, we are covering the most common eight types of chemical reactions, which are part of the class X chemistry syllabus as well.
Decomposition reaction
Combination reaction
Combustion reaction
Neutralization reaction
Single displacement reaction
Double displacement reaction
Precipitation reaction
Redox reaction
Decomposition Reaction – In a decomposition reaction, molecules or compounds break down into two or more than two simpler chemically new substances. For example, electrolysis of water. In the electrolysis of water, water breaks down into hydrogen and oxygen, which show completely different properties than water.
Reaction - 2H2O electricity → 2H2 + O2
Combination Reaction – In a combination reaction, two or more molecules are combined together chemically to form a new substance (compound). Combination and decomposition reactions are opposite of each other. For example, when we burn magnesium ribbon (or magnesium), it gives grey-black ash of magnesium oxide.
Reaction – Mg + O2 → MgO
Combustion Reaction – It is an exothermic reaction that releases energy, generally in the form of heat. It is a reaction between fuel and an oxidant (generally atmospheric oxygen) that produces smoke, water and heat generally. For example, when we burn methane, it gives carbon dioxide and water.
Reaction – CH4 + 2O2 → CO2 + 2H2O
Neutralization Reaction – In these reactions, acid and base react with each other and form salt and water. For example, hydrochloric acid reacts with sodium hydroxide (base) and forms sodium chloride (salt) and water.
Single Displacement Reaction – In these reactions, more reactive metal displaces less reactive metal from its salt. In these reactions, products can be determined through reactivity series. Reactivity series is a series in which elements are arranged in decreasing order of their reactivity. It means the elements present at the top of this reactivity series are more reactive than the elements present at the bottom.
The reaction of potassium with magnesium chloride is an example of a single displacement reaction. In this reaction, potassium displaces magnesium from its salt because potassium is more reactive than magnesium. Potassium is present at the top of the reactivity series and is the most reactive element.
Reaction – 2K + MgCl2 → 2KCl + Mg
Double displacement reaction – In these reactions, two aqueous ionic compounds exchange their ions (mostly cations) and produce two new compounds. For example, potassium nitrate reacts with aluminium chloride and forms aluminium nitrate and potassium chloride.
Reaction – KNO3 + AlCl3 ↔️ Al(NO3)3 + KCl
Precipitation Reaction – In these reactions, an insoluble precipitate is formed. In precipitation reactions, two soluble salts in aqueous solutions are combined and form an insoluble precipitate.
Reaction – AgNO3(aq) + KCl(aq) ↔️ AgCl + KNO3(aq)
Redox Reaction – Those chemical reactions in which oxidation and reduction take place simultaneously are called redox reactions. Oxidation is the addition of oxygen, while reduction is the addition of hydrogen (or removal of oxygen). We have already discussed oxidation and reduction in a separate article with the title ‘Oxidation and Reduction’. You can refer to this article for a detailed explanation of oxidation and reduction.
The reaction of copper oxide with hydrogen is an example of a redox reaction. In this reaction, hydrogen has undergone oxidation by gaining oxygen atoms while copper oxide has undergone reduction by removing oxygen.
List of Common Chemical Reactions
We are giving here a general list of common chemical reactions.
This ends our coverage on a list of Various Types of Chemical Reactions. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to differentiate various reactions easily and it will help you in experiments as well because we have covered almost all-important chemical reactions of Class X Chemistry Experiments.
FAQs on Chemical Reactions
1. What is a chemical reaction as per the CBSE Class 10 syllabus?
A chemical reaction is a process in which one or more substances, known as reactants, are converted into one or more different substances, known as products. This transformation involves the rearrangement of atoms. For example, when we breathe, the glucose in our cells reacts with the oxygen we inhale to produce carbon dioxide, water, and energy, which is a vital chemical reaction for life.
2. What are the main types of chemical reactions with one example each?
The main types of chemical reactions covered in the syllabus include:
- Combination Reaction: Two or more reactants combine to form a single product. Example: The burning of magnesium ribbon in air to form magnesium oxide (2Mg + O₂ → 2MgO).
- Decomposition Reaction: A single compound breaks down into two or more simpler substances. Example: The electrolysis of water to produce hydrogen and oxygen gas (2H₂O → 2H₂ + O₂).
- Single Displacement Reaction: A more reactive element displaces a less reactive element from its compound. Example: Potassium reacting with magnesium chloride to form potassium chloride and magnesium (2K + MgCl₂ → 2KCl + Mg).
- Double Displacement Reaction: Two compounds exchange ions to form two new compounds. Example: The reaction between silver nitrate and potassium chloride to form silver chloride and potassium nitrate (AgNO₃ + KCl → AgCl + KNO₃).
- Precipitation Reaction: A reaction that forms an insoluble solid, called a precipitate. Example: Mixing aqueous solutions of barium chloride and sodium sulphate to form a white precipitate of barium sulphate (BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl).
- Neutralisation Reaction: An acid and a base react to form salt and water. Example: Hydrochloric acid (acid) reacting with sodium hydroxide (base) to form sodium chloride (salt) and water (HCl + NaOH → NaCl + H₂O).
- Combustion Reaction: A substance reacts rapidly with an oxidant, usually oxygen, to produce heat and light. Example: The burning of methane gas (CH₄ + 2O₂ → CO₂ + 2H₂O).
- Redox Reaction: A reaction where oxidation and reduction occur simultaneously.
3. What are some observable signs that indicate a chemical reaction has occurred?
You can often tell a chemical reaction has taken place by observing one or more of the following signs:
- Evolution of a gas: Bubbles are formed, like when zinc reacts with hydrochloric acid to release hydrogen gas.
- Change in colour: The substances may change colour, such as when colourless lead nitrate and potassium iodide react to form a yellow precipitate.
- Formation of a precipitate: An insoluble solid is formed when two solutions are mixed.
- Change in temperature: The reaction mixture may become hotter (exothermic) or colder (endothermic).
- Change in state: A reaction might start with gases and produce a solid, like ammonia gas reacting with hydrogen chloride gas to form solid ammonium chloride.
4. Why is a combination reaction considered the opposite of a decomposition reaction?
A combination reaction is considered the opposite of a decomposition reaction because their processes are reversed. In a combination reaction, two or more simpler substances join together to form a single, more complex compound (A + B → AB). In contrast, a decomposition reaction involves a single, complex compound breaking down into two or more simpler substances (AB → A + B). Essentially, one builds up a compound while the other breaks it down.
5. How does the reactivity series help in predicting the outcome of a single displacement reaction?
The reactivity series is a chart that arranges metals in order of decreasing reactivity. In a single displacement reaction, this series is crucial for predicting whether a reaction will occur. A metal that is higher up in the series (more reactive) can displace a metal that is lower down in the series (less reactive) from its salt solution. For example, since potassium (K) is more reactive than magnesium (Mg), it can displace magnesium from magnesium chloride (MgCl₂). However, the reverse reaction would not happen.
6. What is the key difference between a single displacement and a double displacement reaction?
The key difference lies in what is being exchanged. In a single displacement reaction, a single, more reactive element replaces another element in a compound. It's a competition between two elements. In a double displacement reaction, two different compounds in an aqueous solution exchange ions (usually the cations and anions switch partners) to form two entirely new compounds. It's an exchange between two compounds, not a replacement by a single element.
7. How is respiration an example of a chemical reaction, and what type of reaction is it?
Respiration is a prime example of a chemical reaction because it involves the transformation of substances into new ones with different properties. In cellular respiration, glucose (C₆H₁₂O₆) reacts with oxygen (O₂) to produce carbon dioxide (CO₂), water (H₂O), and energy. Since this process releases a significant amount of energy in the form of heat, it is classified as an exothermic reaction. It is also a type of combustion reaction, where a fuel (glucose) is 'burned' to release energy.
8. Are all reactions that form a solid a precipitation reaction? Explain with an example.
No, not all reactions that form a solid are classified as precipitation reactions. A precipitation reaction specifically refers to a reaction where two aqueous (dissolved in water) solutions are mixed, resulting in the formation of an insoluble solid called a precipitate. For example, mixing aqueous silver nitrate and aqueous sodium chloride forms solid silver chloride. In contrast, a reaction like the burning of a magnesium ribbon (a solid) in air forms magnesium oxide, which is also a solid (ash). However, this is a combination reaction, not a precipitation reaction, because it does not involve the mixing of two aqueous solutions.
