NCERT Solution for Class 10 Science Chapter 1
Chemical Reactions and Equations
Exercises Questions
Page No-15
Questions No-9
What does one mean by exothermic and endothermic reactions? Give examples.
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Exothermic Reaction: Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
For example: Burning of methane in air gives heat and light.
CH₄ (g)+O₂ (g) → CO₂ (g)+2H₂O(g)+heat
Endothermic Reaction: Reactions that absorb energy or require energy in order to proceed are called endothermic reactions. For example: Silver chloride absorb the heat from sunlight and get decomposed into Silver and Chlorine.
2AgCl(s) Sunlight → 2Ag(s)+Cl₂(g)
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Exothermic reaction: A reaction in which energy is released in the form of heat or light.
Eg.: Burning of Natural gas (methane)
CH4(g) + O2(g) → CO2(g) + H2O(l) + Heat
Endothermic reaction: A reaction in which energy is absorbed from the surroundings and cooling is produced.
Eg.: Decomposition of calcium carbonate
CaCO3(s) ————-→ CaO(s) + CO2(g)
Calcium Carbonate Calcium oxide Carbon dioxide
or Lime stone or quick lime
Exothermic reaction- Reaction in which heat is released along with th formation of products.
EX:-Burning of gas
CH4(g)+O2(g) —– CO2(g) H2O(l)+Heat
Methane+Oxygen —— Carbon-dioxide+Water+Heat (∆)
Endothermic reaction:-Reation in which energy is absorbed.
EX:-Decomposition of calcium carbonate.
CaCo3(s) —– CaO(s)+CO2(g)
Calcium carbonate —– Calcium-Oxide+ Carbon-dioxide.
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Exothermic reaction – A reaction in which heat is released is called the exothermic reaction. Burning of fuel is an example of exothermic reaction. When methane is burnt it gives heat along with carbon dioxide and water.
CH4(g) + O2(g) → CO2(g) + H2O(l) + Heat
Endothermic reaction – A reaction in which heat is absorbed is called endothermic reaction. Example – When silver chloride is left in the sunlight, it absorbs heat and turns grey because of formation of silver metal.
2AgCl(s) Sunlight → 2Ag(s)+Cl₂(g)
Exothermic reactions are often associated with a temperature increase in the surroundings.
Common examples of exothermic reactions include combustion reactions (e.g., burning of wood or gasoline), neutralization reactions (e.g., the reaction between an acid and a base to form water and a salt), and many oxidation reactions.
Example: The combustion of methane (CH4) in the presence of oxygen is highly exothermic.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat
Endothermic reactions often result in a decrease in temperature in the surroundings.
Common examples of endothermic reactions include dissolving certain salts in water, the process of photosynthesis, and the evaporation of water.
Example: The dissolution of ammonium nitrate in water is an endothermic process.
NH4NO3(s) + H2O(l) → NH4+ (aq) + NO3- (aq) + heat absorbed
In summary, exothermic reactions release heat and have products with lower energy than the reactants, while endothermic reactions absorb heat and have products with higher energy than the reactants. These terms are essential in understanding the thermodynamics of chemical reactions and how energy is transferred during chemical processes.