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Endothermic Reaction is a chemical reaction in which the reactants absorb the heat energy from the surroundings in order to form different products. These reactions create a cooling effect, as they lower the temperature of their surrounding areas. An example of endothermic physical reactions is the melting of ice cubes as they absorb heat from the surroundings without breaking or forming any chemical bonds.
Key Terms: Endothermic Reaction, Exothermic Reaction, Chemical Bonding, Activation Energy, Chemical reaction, chemical bonds, physical reactions
What is Endothermic Reaction?
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An endothermic reaction is a chemical reaction that absorbs heat from its surroundings. The absorbed energy from the surroundings provides the activation energy for the reaction to take place. For example, water absorbs heat from a burner to be converted into vapor.
When a chemical bond is broken through a reaction, it is usually accompanied by a release of energy. In a similar way, the formation of chemical bonds requires an input of energy. The energy that is released or supplied can be of various forms such as light, heat, and electricity. Endothermic reactions involve the formation of chemical bonds when heat is absorbed from the surroundings. On the other hand, exothermic reactions are chemical reactions that involve the release of heat energy generated from the breakage of bonds.
The video below explains this:
Endothermic Reaction Detailed Video Explanation:
Endothermic Reaction Explanation
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Endothermic reactions are frequently non-spontaneous because they produce more energy products than reactants. The change in enthalpy for an endothermic reaction is always positive.
- The products of an endothermic reaction have more energy than the reactants.
- As a result, the change in enthalpy is positive, and the reaction absorbs heat from the environment.
- The reactions absorb heat from the atmosphere, resulting in a colder temperature in the system where the reaction occurs.
- Furthermore, the enthalpy, which is the difference in heat energy during the transfer of reactants to products, increases as the reaction progresses.
The breaking and formation of chemical bonds change reactants into products in a chemical reaction. One example is the combustion of carbon with oxygen to produce carbon dioxide. Endothermic reactions include a change in positive energy, while exothermic reactions involve a change in negative energy. In an endothermic reaction, more energy is consumed in breaking bonds than is released in producing them, therefore the process progresses with net energy absorption.
Endothermic reactions produce compounds with stored chemical energy in their bonds, which could suddenly discharge in the event of an explosion. Certain chemicals are found in chlorates, perchlorates, and nitrates. When coupled with other materials, they can produce a high-explosive mixture.
Examples of Endothermic Reactions
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Some of the examples of endothermic reactions are –
- Chlorophyll in green plants helps in the conversion of water and carbon dioxide into glucose and oxygen during photosynthesis. That is why it is a supplier of energy.
- In a test tube, a little amount of ammonium chloride is mixed with water. After that, we can see that it cools down in the test tube. As a result, heat is absorbed from the surrounding test tube.
- An endothermic reaction occurs when you cook an egg. The energy from the pan is absorbed to cook the egg.
- An endothermic reaction occurs when ammonium chloride (NH4Cl) is dissolved in water. The ammonium (NH4+) and chloride (Cl–) ions separate from the salt. The following is a representation of the chemical equation: NH4Cl (s) + H2O (l) → NH4Cl (aq) – Heat
- When dissolved in water, ammonium nitrate (NH4NO3), a key component of instant cold packs, splits into the ammonium cation (NH4+) and the nitrate anion (NO3–). By interacting with the OH– and H+ ions in water, these ions generate ammonium hydroxide (NH4OH) and nitric acid (HNO3), respectively. This reaction is endothermic because it absorbs heat from the environment and cools it.
Endothermic Reaction Energy Level Diagram
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Endothermic reactions are depicted in a basic energy level diagram below. The activation energy is the amount of energy that must be delivered to the reactants for them to break through the energy barrier and react. In an endothermic reaction, the result has higher potential energy than the reactants. The energy absorbed by the system during the chemical reaction is represented by this gap in the potential energy.
Read More: Chemical Reaction Important Questions
How are Endothermic and Exothermic Reactions Different?
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The terms ‘Endo’ and ‘Exo’ are derived from Greek words, meaning ‘within’ and ‘out’ respectively. The key difference between endothermic and exothermic reactions is that the endothermic reaction absorbs heat from the surroundings whereas exothermic reactions involve a release of heat.
The differences between endothermic and exothermic reactions are as tabulated below –
| Endothermic Reaction | Exothermic Reaction |
|---|---|
| The system absorbs the heat from the surroundings | The system releases heat into the surroundings |
| Enthalpy change (ΔH) is positive | The enthalpy change, ΔH is negative |
| The entropy of the surroundings decreases (ΔS < 0) | The entropy of the surroundings increases (ΔS > 0) |
Things to Remember
- Endothermic Reactions are chemical reactions that absorb heat from the surroundings they occur in.
- Dissolving ammonium chloride in water is an example of an endothermic reaction.
- Endothermic processes include cooking an egg, melting ice cubes, etc.
- In an endothermic reaction, the potential energy of the product is higher than that of its reactants.
- The human body uses the endothermic nature of the process of evaporation to cool itself.
Sample Questions
Ques. What type of Energy Transfer occurs during an Endothermic Reaction? (1 mark)
Ans. Chemical energy to kinetic energy is the answer. In an endothermic process, heat is absorbed and subsequently transformed into chemical energy. Temperature is the unit of measurement for heat, not energy.
Ques. How can we know whether a reaction is endothermic or exothermic? (5 marks)
Ans. Exothermic Reaction: The chemical reactions that move forward with the release of heat energy are known as exothermic reactions. Example:
Carbon burns in oxygen to form carbon dioxide and heat energy is produced.
C + O2 → CO2 + Heat
Endothermic Reaction: The chemical reactions that move forward by absorbing heat energy are known as endothermic reactions. Example:
When nitrogen and oxygen are heated together to a temperature of about 3000oC, a nitric oxide gas is produced.
N2 + O2 + Heat → 2NO
In exothermic reactions, heat is released and in endothermic heat is absorbed, in this way one can easily find out the type of reaction.
Ques. Is it true that frying an egg produces an endothermic reaction? (1 mark)
Ans. An endothermic reaction occurs when an egg is cooked. When energy is taken from the environment in the form of heat, an endothermic process occurs. In this situation, the egg absorbs heat energy from the pan.
Ques. State whether the given reaction is an endothermic or exothermic reaction – Ba(OH)2 + NH4Cl -→ BaCl2 + 2NH4OH (2 marks)
Ans. In this reaction, a fall in temperature is observed. Hence, heat is released in this reaction, and therefore it is an endothermic reaction.
Ques. What are the signs that a reaction is endothermic? (1 mark)
Ans. If the enthalpy change for a reaction is positive, the reaction is endothermic (endo- = in), meaning it absorbs heat as it continues.
Ques. What are the two important facts about endothermic reactions? (2 marks)
Ans. In an endothermic reaction, more energy is consumed in breaking bonds than is released in creating them, hence the reaction proceeds with net energy absorption.
Endothermic reaction chemicals have chemical energy stored or potential in their bonds, which can be released spontaneously in an explosion.
Ques. Is baking a cake considered an endothermic reaction? (1 mark)
Ans. An endothermic chemical reaction occurs when you bake a cake, changing the ooey-gooey batter into a fluffy, delectable delicacy.
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