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ICSE Class 9 Chemistry Question 9 of 18

Chemical Changes & Reactions — Question 17

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Question

Question 17

Explain the term energy changes in a chemical change or reaction. Give an example with a balanced equation, for each of the following reactions:

(a) exothermic reaction

(b) endothermic reaction

(c) photochemical reaction

(d) electrochemical reaction.

Answer

The difference between the chemical energy of the reactants and the products is known as the energy changes in a chemical change or reaction.

Example of :

(a) exothermic reaction:
     2H2 + O2 ⇌Δ\xrightleftharpoons{\enspace\Delta\enspace} H2O + ΔT

(b) endothermic reaction:
     N2 + O2 ⇌Δ\xrightleftharpoons{\enspace\Delta\enspace} 2NO - ΔT

(c) photochemical reaction:
     H2 + Cl2 →sunlight\xrightarrow{\text{sunlight}} 2HCl
     Slow reaction in diffused light
     Explosive reaction in direct sunlight

(d) electrochemical reaction:
     2H2O[acidified]→CurrentElectric2H2[cathode]+O2[anode]\underset{\text{[acidified]}}{2\text{H}_2\text{O}} \xrightarrow[\text{Current}]{\text{Electric}} \underset{\text{[cathode]}}{2\text{H}_2} + \underset{\text{[anode]}}{\text{O}_2}