Examples of Endothermic Reactions with Equations

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Endothermic reactions, a fundamental concept in chemistry, are characterized by the absorption of heat from the surroundings to proceed. These reactions are essential in various natural phenomena and industrial processes, driving transformations by taking in energy from their environment. Below, we delve into ten diverse examples of endothermic reactions, each accompanied by its respective chemical equation.

1. Photosynthesis:
\(6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\)
Photosynthesis, a vital process for plants and other autotrophic organisms, is a prime example of an endothermic reaction. During this process, carbon dioxide and water molecules absorb energy from sunlight to produce glucose and oxygen.
2. Melting of Ice:
\(H_2\text{O}(s) \rightarrow H_2\text{O}(l) + \text{heat}\)
The melting of ice is another common example of an endothermic reaction. Solid water (ice) absorbs heat energy from its surroundings to transition into liquid water.
3. Evaporation of Water:
\(H_2\text{O}(l) \rightarrow H_2\text{O}(g) + \text{heat}\)
When liquid water evaporates, it absorbs heat from the surroundings to transform into water vapour. This endothermic process is essential for the water cycle and various cooling mechanisms.
4. Dissolution of Ammonium Nitrate:
\(NH_4NO_3(s) + \text{heat} \rightarrow NH_4^+(aq) + NO_3^-(aq)\)
The dissolution of ammonium nitrate in water is an example of endothermic reaction. As solid ammonium nitrate dissolves, it absorbs heat from its surroundings, causing a decrease in temperature.
5. Thermal Decomposition of Calcium Carbonate:
\(CaCO_3(s) + \text{heat} \rightarrow CaO(s) + CO_2(g)\)
On warming Calcium carbonate decays to form calcium oxide and carbon dioxide. This process, observed in activities such as limestone calcination, requires the input of heat energy.
6. Endothermic Reaction of Barium Hydroxide Octahydrate with Ammonium Chloride:
\(Ba(OH)_2.8H_2O(s) + 2NH_4Cl(s) + \text{heat} \rightarrow BaCl_2(aq) + 2NH_3(g) + 10H_2O(l)\)
Mixing solid barium hydroxide octahydrate with solid ammonium chloride results in an endothermic reaction. Heat is absorbed from the surroundings, leading to the formation of aqueous barium chloride, ammonia gas, and water.
7. Reaction of Potassium Chloride with Water:
\(KCl(s) + H_2O(l) + \text{heat} \rightarrow KCl(aq)\)
When solid potassium chloride dissolves in water, it absorbs heat from its surroundings, making it an endothermic process. This dissolution reaction is commonly used in heat packs for therapeutic purposes.
8. Dissociation of Ammonium Nitrate in Water:
\(NH_4NO_3(s) + \text{heat} \rightarrow NH_4^+(aq) + NO_3^-(aq)\)
Similar to the dissolution of other salts, the dissociation of ammonium nitrate into its constituent ions in water is an endothermic reaction. Heat is absorbed during this process, resulting in a cooling effect.
9. Reaction of Barium Hydroxide Octahydrate with Solid Ammonium Chloride:
\(Ba(OH)_2.8H_2O(s) + 2NH_4Cl(s) + \text{heat} \rightarrow BaCl_2(aq) + 2NH_3(g) + 10H_2O(l)\)

When solid barium hydroxide octahydrate reacts with solid ammonium chloride, an endothermic reaction occurs. The reaction absorbs heat from the surroundings, leading to the formation of aqueous barium chloride, ammonia gas, and water.
10. Dissociation of Ammonium Thiocyanate in Water:
\(NH_4SCN(s) + \text{heat} \rightarrow NH_4^+(aq) + SCN^-(aq)\)
The dissolution of solid ammonium thiocyanate in water is an endothermic process. As the compound dissociates into its ions, heat is absorbed from the surroundings, causing a decrease in temperature.
So, endothermic reactions play a crucial role in various chemical processes, ranging from biological functions like photosynthesis to industrial applications like cooling systems. Understanding these reactions and their associated equations is essential for comprehending the fundamental principles of chemistry and their practical implications.

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