Question

In which of the following reactions heat energy is absorbed?

• A. Combustion of coal
• B. The reaction of barium hydroxide with ammonium chloride
• C. On dissolving ammonium chloride in water
• D. Both b and c

Answer 1

The correct option is B

The reaction of barium hydroxide with ammonium chloride

The explanation for the correct option-

• The reaction of barium hydroxide with ammonium chloride results in the absorption of heat.
• This reaction is a decomposition reaction and involves the requirement of heat and is an endothermic process.
• Reaction- when barium hydroxide reacts with ammonium chloride, it forms barium chloride + ammonium hydroxide and involves a lot of heat.

$\underset{\mathrm{Barium}\mathrm{hydroixde}}{\mathrm{Ba}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonium}\mathrm{chloride}}{2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Barium}\mathrm{chloride}}{{\mathrm{BaCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonium}\mathrm{hydroixde}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)}$

The explanation for the incorrect option:

Option A:
Combustion of coal is an exothermic reaction which means heat is given off and it produces an oxidized gaseous product as a mixture known as smoke

${\mathrm{CH}}_4\left(\mathrm{g}\right)+2{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Option C:

The dissolution of ammonium chloride in water is endothermic but it is a very spontaneous process.

Since$∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$

Hence, the correct option - (B), the reaction of barium hydroxide with ammonium chloride, heat energy is absorbed.