Question

In which of the following, heat energy will be evolved?

• A. 1) Electrolysis of water
• B. (2) Dissolution of ${\mathrm{NH}}_4\mathrm{Cl}$in water
• C. (3) Burning of L.P.G.
• D. (4) Decomposition of$\mathrm{AgBr}$ in the presence of sunlight

Answer 1

The correct option is C

(3) Burning of L.P.G.

Explanation for correct answer

Correct answer: (3) Burning of L.P.G

• Heat of combustion is total amount of heat released when a fuel is completely combusted in the presence of oxygen.
• It is an exothermic reaction, hence, it releases heat.
• It is a chemical reaction in which hydrocarbon is burnt, and it produces carbon dioxide, heat and water.
• Fuels releases heat on burning.

Hence, option 3 is correct.

Explanation for Incorrect answer

1. Electrolysis is the breakdown of water in the presence of electricity, it also absorbs heat. Hence, option (1) is incorrect.
2. Dissolution of ${\mathrm{NH}}_4\mathrm{Cl}$in water dissolution reaction of ammonium chloride is an endothermic process. Hence, option 2 is incorrect.

4. Decomposition of $\mathrm{AgBr}$ in the presence of sunlight to produce silver metal and a halogen gas ( bromine gas). Thus, Silver chloride undergoes decomposition in presence of sunlight and it does not evolve heat. Therefore, option 4 is incorrect.