Types of Chemical Reactions

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Jasmine Grover

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A chemical reaction is a transformative process where reactants change, forming new products. This transformation involves the movement of electrons, the breaking of existing bonds, and the formation of new bonds, resulting in the creation of desired products and sometimes by-products. Chemistry revolves around the interactions between elements and compounds, specifically through bonds and reactions.

  • There are mainly 8 types of chemical reactions.
  • The types of chemical reactions are based its characteristics.
  • Some common types of reactions are Combination reaction, Decomposition reaction, Displacement reaction and Double displacement reaction.

Key Terms-: Chemical Reaction, Decomposition, Combination, Combustion, Neutralization, Single Displacement, Double Displacement, Precipitation, Redox.


What is Chemical Reaction?

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A chemical reaction is a process where two or more elements or compounds interact with each other, leading to the formation of a product. The substances involved in the reaction are referred to as reactants.

 

  • In a chemical reaction, bonds between atoms are broken and new bonds are formed, resulting in the formation of the desired product.
  • The rate at which a chemical reaction occurs is known as the rate of reaction.
  • It depends on various factors such as the concentration of reactants, pressure, and temperature. 
  • As a result of the chemical reaction, the original properties of the reactants change, leading to the formation of products with different properties.

Read More: Oxides of Nitrogen


Characteristics of a Chemical Reaction 

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Some characteristics of Chemical Reaction are mentioned below:

Evolution of Gas

Certain chemical reactions result in the release of gas. For instance, when zinc reacts with hydrochloric acid, hydrogen gas is produced as a byproduct, while zinc chloride is formed.

  • Reaction- Zn + 2HCl → ZnCl2 + H2

Change in Colour 

Certain chemical reactions are characterized by a noticeable change in color. For instance, when a colorless substance like lead nitrate reacts with potassium iodide, it results in the formation of a yellow precipitate of lead iodide and colorless potassium nitrate.

  • Reaction- Pb(NO3)2 + 2KI → PbI2 + 2KNO3

Change in Temperature

 

Certain chemical reactions are accompanied by temperature changes. For instance, some reactions release heat, known as exothermic reactions, while others absorb heat, known as endothermic reactions.

Change in Energy 

Chemical reactions frequently involve an alteration in energy. In the course of a chemical reaction, energy can either be released or absorbed. For instance, in combustion reactions, energy is liberated through processes like the burning of fuel.

Formation of Precipitate 

Certain chemical reactions result in the formation of a precipitate. One such example is the reaction between barium chloride and sodium sulfate, which leads to the formation of sodium chloride and a precipitate of barium sulfate.

  • Reaction- BaCl2 + Na2SO4 → BaSO4 + NaCl

Change in State 

Certain chemical reactions involve a transition in the physical state of substances. One such example is the reaction between ammonia gas and hydrogen chloride gas, which results in the formation of solid ammonium chloride crystals.

  • Reaction- NH3(g) + HCl(g) → NH4Cl(s)

Read More: Difference Between Oxidation and Reduction


Types of Chemical Reactions 

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Here are the types of Chemical Reactions:

Combination Reaction 

A combination reaction is a type of chemical reaction where two or more substances combine to form a new substance. 

  • This is also known as a synthesis reaction. 
  • In a combination reaction, the reactants are typically elements or simple compounds, and the product is a more complex compound.
  • Reaction- Mg + O2 → MgO

In the following reaction, sodium undergoes a reaction with chlorine to produce sodium chloride as the resulting product.

2Na(s) + Cl2(g) → 2NaCl(s)

Decomposition Reaction 

A decomposition reaction is a chemical reaction in which one reactant breaks down into two or more products. 

  • This can happen when the reactant is heated, exposed to light, or passed through an electric current.
  • For example, when water is decomposed by electrolysis, it breaks down into hydrogen and oxygen gas. 
  • This reaction can be represented by the following equation:

Reaction - 2H2O electricity → 2H2 + O2

  • In the below reaction, calcium carbonate is decomposed and forms calcium carbonate and carbon dioxide in gaseous form.

CaCO3 → CaO + CO2

Read More: Electrochemical Cells

Combustion Reaction 

Combustion is a chemical reaction that occurs when a fuel reacts with oxygen to produce heat and light. 

  • The fuel is typically a hydrocarbon, which is a compound made up of carbon and hydrogen. 
  • When a hydrocarbon burns, the carbon and hydrogen atoms in the fuel react with oxygen atoms in the air to form carbon dioxide and water. 
  • This reaction releases a large amount of energy, which is why combustion is used to power cars, stoves, and other devices.

Reaction- CH4 + 2O2 → CO2 + 2H2O

Neutralisation Reaction 

A neutralisation reaction is a chemical reaction between an acid and a base. When an acid and a base react, they neutralise each other, meaning that they cancel out each other's properties. 

  • Acids are sour and have a pH below 7, while bases are bitter and have a pH above 7.
  • When an acid and a base react, they produce salt and water. 
  • The salt is a neutral substance, meaning that it has a pH of 7.

An example of a commonly observed neutralisation reaction involves the interaction between hydrochloric acid, a strong acid, and sodium hydroxide, a strong base.

HCl + NaOH → NaCl + H2O

Single Displacement Reaction 

A single displacement reaction is a chemical reaction in which one element replaces another element in a compound

  • This happens when the element that is being replaced is less reactive than the element that is doing the replacing. 
  • For example, if you put a piece of zinc in a solution of copper sulfate.
  • The zinc will replace the copper in the solution, forming zinc sulfate and copper metal.

Zn + CuSO4 → ZnSO4 + Cu

An illustration of this type of reaction is the reaction between potassium and magnesium chloride, which is a single displacement reaction. 

  • In this reaction, potassium displaces magnesium from its salt because potassium is more reactive than magnesium. 
  • Potassium, being at the top of the reactivity series, is the most reactive element.

2K + MgCl2 → 2KCl + Mg

Double displacement reaction 

A double displacement reaction is a type of chemical reaction in which two compounds exchange their ions to form two new compounds. This type of reaction is often called a "salt metathesis reaction" or a "double decomposition reaction."

KNO3 + AlCl3 ↔ Al(NO3)3 + KCl

Precipitation Reaction 

A precipitation reaction is a chemical reaction that occurs when two solutions are mixed and one of the products is an insoluble solid, called a precipitate. The precipitate is formed when the ions in the two solutions combine to form an insoluble compound.

  • The typical precipitation reactions that occur in an aqueous solution involve the creation of an insoluble ionic compound 
  • When two solutions containing soluble compounds are combined. 
  • For example, when an aqueous solution of NaCl is mixed with an aqueous solution of AgNO3
  • The first solution contains hydrated Na+ and Cl ions, while the second solution contains Ag+ and NO3 ions.
  1.  NaCl(s) → Na+(aq) + Cl(aq)
  2. AgNO3(s) → Ag+(aq) + NO3(aq)

Redox Reaction 

In a redox reaction, one reactant is oxidized and the other reactant is reduced.The oxidized reactant loses electrons and becomes more positively charged, while the reduced reactant gains electrons and becomes more negatively charged.

  • An example of a redox reaction is the reaction between copper oxide and hydrogen. 
  • In this reaction, hydrogen undergoes oxidation by gaining oxygen atoms, while copper oxide undergoes reduction by losing oxygen atoms.

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Things To Remember

  • In a synthesis reaction, two or more substances combine to form a new compound.
  • A decomposition reaction is the opposite of synthesis, where a compound breaks down into simpler substances.
  • Combustion reactions involve a substance reacting with oxygen to produce heat and light, often resulting in the formation of carbon dioxide and water.
  • In an acid-base reaction, an acid and a base react to form salt and water.
  • Oxidation-reduction (redox) reactions involve the transfer of electrons from one substance to another.
  • Precipitation reactions occur when two solutions react to form a solid substance called a precipitate.
  • In a displacement reaction, an element in a compound is replaced by another element.
  • A neutralization reaction happens when an acid and a base react to neutralize each other and form salt and water.
  • In a double displacement reaction, the positive and negative ions of two compounds switch places to form new compounds.

Sample Questions

Ques: What is a synthesis reaction? (2 Marks)

Ans: A synthesis reaction is a type of chemical reaction where two or more substances combine to form a new compound. An example is the reaction between hydrogen and oxygen to form water: 2H2 + O2 → 2H2O.

Ques: What is a decomposition reaction? (2 Marks)

Ans: A decomposition reaction is a chemical reaction where a compound breaks down into simpler substances. An example is the decomposition of hydrogen peroxide into water and oxygen gas: 2H2O2 → 2H2O + O2.

Ques: What is a combustion reaction? (3 Marks)

Ans: A combustion reaction is a reaction in which a substance reacts with oxygen, usually producing heat and light. For example, the combustion of methane (CH4) in the presence of oxygen produces carbon dioxide (CO2) and water (H2O): CH4 + 2O2 → CO2 + 2H2O.

Ques: What is an acid-base reaction? (3 Marks)

Ans: An acid-base reaction is a type of chemical reaction that occurs when an acid reacts with a base, resulting in the formation of salt and water. One example is the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) to produce sodium chloride (NaCl) and water (H2O): HCl + NaOH → NaCl + H2O.

Ques: What is an oxidation-reduction (redox) reaction? (3 Marks)

Ans: An oxidation-reduction (redox) reaction is a type of chemical reaction where there is a transfer of electrons between species. One example is the reaction between iron (Fe) and oxygen (O2) to form iron oxide (Fe2O3), commonly known as rust: 4Fe + 3O2 → 2Fe2O3.

Ques: What is a precipitation reaction? (3 Marks)

Ans: A precipitation reaction occurs when two solutions are mixed, and a solid substance called a precipitate is formed. For instance, when silver nitrate (AgNO3) is mixed with sodium chloride (NaCl), silver chloride (AgCl) precipitates: AgNO3 + NaCl → AgCl + NaNO3.

Ques: What is a displacement reaction? (3 Marks)

Ans: A displacement reaction is a reaction where one element in a compound is replaced by another element. An example is the reaction between zinc (Zn) and hydrochloric acid (HCl) to produce zinc chloride (ZnCl2) and hydrogen gas (H2): Zn + 2HCl → ZnCl2 + H2.

Ques: What is a neutralization reaction? (3 Marks)

Ans: A neutralization reaction occurs when an acid reacts with a base to form salt and water. An example is the reaction between sulfuric acid (H2SO4) and sodium hydroxide (NaOH) to produce sodium sulfate (Na2SO4) and water (H2O): H2SO4 + 2NaOH → Na2SO4 + 2H2O.

Ques: What is a double displacement reaction? (3 Marks)

Ans: A double displacement reaction is a reaction where the positive and negative ions of two compounds switch places to form new compounds. One example is the reaction between lead nitrate (Pb(NO3)2) and potassium iodide (KI), which forms lead iodide (PbI2) and potassium nitrate (KNO3): Pb(NO3)2 + 2KI → PbI2 + 2KNO3.

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CBSE X Related Questions

1.
Oil and fat containing food items are flushed with nitrogen. Why?

      2.
      Which of the statements about the reaction below are incorrect?
      \(\text{ 2PbO(s) + C(s) → 2Pb(s) + C}O_2\text{(g)}\)
      (a) Lead is getting reduced. 
      (b) Carbon dioxide is getting oxidized. 
      (c) Carbon is getting oxidized. 
      (d) Lead oxide is getting reduced.

        • (a) and (b)

        • (a) and (c)

        • (a), (b) and (c)
        • all

        3.
        Why does the sky appear dark instead of blue to an astronaut?

            4.
            State two ways to prevent the rusting of iron.

                5.
                Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s−1.

                    6.
                    Explain the following in terms of gain or loss of oxygen with two examples each. 
                    (a) Oxidation
                    (b) Reduction

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