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Chemical Reactions and Equations - Identify endothermic, exothermic, oxidation, and reduction processes

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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An Exothermic Reaction is a chemical reaction in which heat is released along with the formation of products. For example, the combustion of natural gas: CH4(g)+2O2(g)→CO2(g)+2H2O(g)+HeatCH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g) + \text{Heat}.

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An Endothermic Reaction is a reaction in which energy is absorbed from the surroundings, usually in the form of heat, light, or electricity. Most decomposition reactions are endothermic, such as CaCO3(s)→ΔCaO(s)+CO2(g)CaCO_3(s) \xrightarrow{\Delta} CaO(s) + CO_2(g).

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Oxidation is defined as the addition of oxygen to a substance or the removal of hydrogen from a substance during a reaction.

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Reduction is defined as the removal of oxygen from a substance or the addition of hydrogen to a substance during a reaction.

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A Redox Reaction (Reduction-Oxidation) occurs when one reactant gets oxidized while the other gets reduced simultaneously in the same reaction.

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The Oxidizing Agent is the substance that provides oxygen for oxidation or removes hydrogen (it gets reduced itself).

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The Reducing Agent is the substance that removes oxygen or provides hydrogen for reduction (it gets oxidized itself).

📐Formulae

Exothermic: Reactants→Products+Heat energy\text{Exothermic: } \text{Reactants} \rightarrow \text{Products} + \text{Heat energy}

Endothermic: Reactants+Heat energy→Products\text{Endothermic: } \text{Reactants} + \text{Heat energy} \rightarrow \text{Products}

Oxidation: Addition of O2 or Removal of H2\text{Oxidation: } \text{Addition of } O_2 \text{ or Removal of } H_2

Reduction: Removal of O2 or Addition of H2\text{Reduction: } \text{Removal of } O_2 \text{ or Addition of } H_2

💡Examples

Problem 1:

Identify the substance oxidized and the substance reduced in the following reaction: CuO(s)+H2(g)→ΔCu(s)+H2O(g)CuO(s) + H_2(g) \xrightarrow{\Delta} Cu(s) + H_2O(g)

Solution:

Substance Oxidized: H2H_2, Substance Reduced: CuOCuO

Explanation:

In this reaction, CuOCuO loses oxygen to become CuCu, so CuOCuO is reduced. H2H_2 gains oxygen to become H2OH_2O, so H2H_2 is oxidized. Here, CuOCuO is the oxidizing agent and H2H_2 is the reducing agent.

Problem 2:

Identify the type of reaction (Endothermic/Exothermic) for: (i) Respiration, (ii) Decomposition of Silver Chloride in sunlight.

Solution:

(i) Exothermic, (ii) Endothermic

Explanation:

(i) Respiration is exothermic because energy is released during the oxidation of glucose: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}. (ii) Decomposition of AgClAgCl is endothermic because it absorbs light energy: 2AgCl(s)→Sunlight2Ag(s)+Cl2(g)2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g).

Problem 3:

In the reaction MnO2+4HCl→MnCl2+2H2O+Cl2MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2, identify the oxidizing agent.

Solution:

MnO2MnO_2 is the oxidizing agent.

Explanation:

HClHCl is oxidized to Cl2Cl_2 (removal of hydrogen), and MnO2MnO_2 is reduced to MnCl2MnCl_2 (removal of oxygen). Since MnO2MnO_2 undergoes reduction, it acts as the oxidizing agent.