Endothermic Reaction - Definition, Examples, Differences, FAQs

Q: AgBr is decomposed into Ag and Br2 in the presence of heat. Write the type of the reaction along with a balanced chemical equation.

2AgBr 2Ag + Br 2 This is an endothermic reaction example.

Q: Q:4) Given a balanced chemical equation:

2HBr H 2 + Br 2 BOND BOND ENERGY(kJ/mol) H-Br 336 H-H 436 Br-Br 193 Calculate the enthalpy change and comment on the type of reaction. Answer: enthalpy change is given by the formula- ∆Htotal = ∆ Hproduct - ∆ Hreactant = - (436+193) kJ/mol - (2x-336) kJ/mol = (-629 + 732) kJ/mol = +103 kJ/mol It is an endothermic reaction.

Q: Comment on the type of reaction: formation of cation from an atom in the gas phase.

X (g) + heat X+(g) + e - Here, ionization is happening. The energy required to remove an electron from its valence orbital in the gaseous phase is called ionization energy. Since there is an attractive force between electron and nucleus in an atom, we need to break that force. Therefore, the formation of cation from an atom in the gas phase is an example for endothermic reaction.

Endothermic Reaction - Definition, Examples, Differences, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:32 PM IST

Define Endothermic Reaction.

To understand this concept, we need to keep in mind the following things:
1) Bond breaking requires energy
2) Bond formation releases energy
Let us consider an example, the reaction of vinegar and baking soda results in the formation of sodium acetate, water and carbon-di-oxide. Before forming the products, atoms of the molecules need to rearrange themselves. Atoms are attracted to one other; therefore, it requires energy to pull them apart. The rearrangement of the atoms of molecules gives us the product. Different amounts of energy are required to form the molecules in the reactant and the product side. Comparing its energy difference insights us into whether a chemical reaction is absorbing or releasing energy.

This Story also Contains

Define Endothermic Reaction.
What is an Endothermic Reaction?
How to Identify Exothermic and Endothermic Reactions?
Difference Between Exothermic Reaction and Endothermic Reaction
Endothermic Reaction Examples Equations.
Energy Diagram

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What is an Endothermic Reaction?

Endothermic Reaction Definition: Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products. The reactions lower the temperature of their surrounding area, thereby creating a cooling effect.

How to Identify Exothermic and Endothermic Reactions?

We can't observe bond breaking and formation, but we can do the following to distinguish between exothermic and endothermic reactions:

1) Temperature change can be monitored using a thermometer. Endothermic reactions happen with a decrease in temperature as it takes energy from the system. When the system temperature is increased, we can note it down as an exothermic reaction.

2) Enthalpy change:

The summation of energy used in reactant bond breaking and energy used in product bond making is known as enthalpy. It is a measure of internal energy. The energy released in breaking a bond in the reactant is always positive and negative during bond making on the product side.

If enthalpy change (∆H) is negative, an exothermic reaction occurs because more energy is released while forming the product than breaking it.

If enthalpy change (∆H) is positive, more energy is consumed to break the bond on the reactant side, and less energy is released when products are formed; then endothermic reaction takes place.

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Difference Between Exothermic Reaction and Endothermic Reaction

1) Endothermic process examples reaction absorbs energy from the surrounding

Exothermic reaction liberates energy to the surrounding.

2) Temperature decreases in case of endothermic reaction while temperature increases in an exothermic reaction

3) Potential energy of the product side is higher in an endothermic reaction. And, the potential energy of the reactant side is greater than the product side in case of an exothermic reaction.

4) Surrounding entropy decreases in an endothermic reaction, and entropy increases in an exothermic reaction.

Endothermic Reaction Examples Equations.

1) Photosynthesis is responsible for the existence of living beings. This is an endothermic process because green plants absorb energy from the sunlight (surrounding) to yield glucose and oxygen.

2) Melting of ice is an endothermic process. Water molecules are packed in a rigid form in the ice. It absorbs energy from the surroundings as heat. Water molecules move faster as the temperature increases and ice melts down.

3) Baking bread and cooking eggs are also endothermic processes; energy is absorbed from the oven or pan to cook it.

4) Sublimation of dry ice: sublimation occurs at a temperature and pressure below the critical point. The phase change requires energy to convert from a solid to a gas phase.

5) Instant ice pack to treat injuries.

SOME OTHER ENDOTHERMIC REACTION EQUATIONS:

1) N₂(g) + O₂(g) +heat 2NO(g)

2) MgCO₃+ heat MgO+ CO₂

3) NH₄NO₃ + heat NH₄⁺ + NO₃^-

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Energy Diagram

NCERT Chemistry Notes :

In chemistry, there is an energy profile showing relative potential energy with time. It is based on the fact that energy changes in bond breaking and bond formation. While bond formation, bonds can be first partially broken and partially formed. This is called the transition state, which is more significant in energy than both reactant and product energy. It is an unstable state, and energy is required to cross the barrier to reach the product formation side. The minimum energy needed to cross this barrier is called activation energy.

This minimum energy is the energy difference between reactant and transition state. The relation between the activation energy and enthalpy change for any chemical reaction can be determined from the energy profile. In endothermic reactions, the overall ∆H is positive because energy is provided to cross the energy barrier, and the product is less stable. In an exothermic reaction, the potential energy of the product is less compared to the reactant. Hence, the product is more stable in case of an exothermic process.

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Frequently Asked Questions (FAQs)

1. Suggest with one word which type of reaction is this: Calcium carbonate is strongly heated in a kiln and give the products calcium oxide and carbon-di-oxide.

Endothermic process because energy is provided to perform the reaction that eventually breaks the bond and rearranges to give us the product.

2. An activity was performed by a teacher. She mixed citric acid and sodium hydrogen carbonate in a beaker and stirred with a glass rod. The beaker was placed on a wood containing few droplets of water. After a moment, the water gets cold. Identify the type

The reaction must be endothermic because it takes energy from the surroundings. Here, it takes it from the water also thereby decreasing its temperature.

3. AgBr is decomposed into Ag and Br2 in the presence of heat. Write the type of the reaction along with a balanced chemical equation.

2AgBr 2Ag + Br₂

This is an endothermic reaction example.

4. Q:4) Given a balanced chemical equation:

2HBr H₂ + Br₂

BOND	BOND ENERGY(kJ/mol)
H-Br	336
H-H	436
Br-Br	193

Calculate the enthalpy change and comment on the type of reaction.

Answer: enthalpy change is given by the formula-

∆Htotal = ∆ Hproduct - ∆ Hreactant

= - (436+193) kJ/mol - (2x-336) kJ/mol

= (-629 + 732) kJ/mol

= +103 kJ/mol

It is an endothermic reaction.

5. Comment on the type of reaction: formation of cation from an atom in the gas phase.

X (g) + heat X+(g) + e^-

Here, ionization is happening. The energy required to remove an electron from its valence orbital in the gaseous phase is called ionization energy.

Since there is an attractive force between electron and nucleus in an atom, we need to break that force.

Therefore, the formation of cation from an atom in the gas phase is an example for endothermic reaction.

6. Can you explain the concept of 'enthalpy of formation' in relation to endothermic reactions?

The enthalpy of formation is the heat change when one mole of a compound is formed from its elements in their standard states. For some compounds, this process is endothermic, meaning they have a positive standard enthalpy of formation. These compounds store energy and are less stable than their constituent elements.

7. How do endothermic reactions relate to the concept of 'chemical potential'?

Endothermic reactions generally increase the chemical potential of the system. As the system absorbs energy, the products have a higher energy state and thus a higher chemical potential than the reactants. This increase in chemical potential can drive further reactions or processes.

8. What is the significance of endothermic reactions in the field of materials science?

In materials science, endothermic reactions are important for:

9. How do endothermic reactions contribute to climate regulation on Earth?

Endothermic reactions play a crucial role in Earth's climate regulation:

10. Can you explain how endothermic reactions are used in chemical analysis techniques?

Endothermic reactions are used in various analytical techniques:

11. What is the difference between endothermic and exothermic reactions?

The main difference is in the direction of heat flow. Endothermic reactions absorb heat from the surroundings, while exothermic reactions release heat to the surroundings. Endothermic reactions result in a temperature decrease, while exothermic reactions cause a temperature increase in the surroundings.

12. How does an endothermic reaction affect the temperature of its surroundings?

An endothermic reaction causes the temperature of its surroundings to decrease. As the reaction absorbs heat energy from the environment, it leaves the surroundings cooler than before the reaction started.

13. How do endothermic reactions affect the surroundings on a molecular level?

On a molecular level, endothermic reactions absorb thermal energy from the surrounding molecules. This causes the surrounding molecules to slow down their motion, resulting in a decrease in their kinetic energy and, consequently, a lower temperature in the surroundings.

14. What is the relationship between bond breaking and bond formation in endothermic reactions?

In endothermic reactions, the energy required to break bonds in the reactants is greater than the energy released when forming new bonds in the products. This net energy difference is what causes the reaction to absorb heat from the surroundings.

15. Can you explain the concept of 'enthalpy of reaction' in the context of endothermic processes?

The enthalpy of reaction (ΔH) for an endothermic process is positive. It represents the amount of heat energy absorbed by the system from the surroundings at constant pressure. This value indicates how much energy is required for the reaction to occur and is typically expressed in units of kJ/mol.

16. Can you provide some everyday examples of endothermic reactions?

Common examples of endothermic reactions include:

17. Can you explain the concept of 'cold packs' using endothermic reactions?

Cold packs used for injuries work on the principle of endothermic reactions. When activated, typically by breaking an inner bag, two chemicals mix and undergo an endothermic reaction. This reaction absorbs heat from its surroundings, including the injured area, providing a cooling effect.

18. How do endothermic reactions contribute to cooling in refrigeration systems?

Refrigeration systems use endothermic processes, particularly the evaporation of a refrigerant. As the refrigerant evaporates, it absorbs heat from its surroundings (the inside of the refrigerator), causing a cooling effect. This endothermic process is key to maintaining low temperatures in refrigerators and air conditioners.

19. How does Le Chatelier's Principle apply to endothermic reactions?

According to Le Chatelier's Principle, increasing the temperature of an endothermic reaction system will shift the equilibrium towards the products, favoring the forward reaction. Conversely, decreasing the temperature will shift the equilibrium towards the reactants.

20. Can endothermic reactions occur spontaneously?

Yes, endothermic reactions can occur spontaneously, but only if the increase in entropy (disorder) of the system is large enough to overcome the unfavorable enthalpy change. This is more likely to happen at higher temperatures where the entropy factor becomes more significant.

21. Can you explain the energy changes in an endothermic reaction using a simple diagram?

In an endothermic reaction, the energy diagram shows the products at a higher energy level than the reactants. The difference in energy levels represents the amount of heat absorbed from the surroundings. The activation energy "hill" between reactants and products is typically higher than in exothermic reactions.

22. What role does enthalpy play in endothermic reactions?

In endothermic reactions, the enthalpy change (ΔH) is positive. This means the final enthalpy of the products is higher than the initial enthalpy of the reactants. The positive ΔH indicates that heat is absorbed by the system from the surroundings during the reaction.

23. How does the First Law of Thermodynamics relate to endothermic reactions?

The First Law of Thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. In endothermic reactions, energy is not created but rather absorbed from the surroundings and converted into chemical potential energy within the products.

24. How do endothermic reactions affect the internal energy of a system?

Endothermic reactions increase the internal energy of a system. As heat is absorbed from the surroundings, the kinetic and potential energy of the particles within the system increase, resulting in a higher overall internal energy.

25. Why do endothermic reactions often feel cold to the touch?

Endothermic reactions feel cold because they absorb heat energy from their surroundings, including your skin. When you touch a container where an endothermic reaction is occurring, heat from your hand is absorbed by the reaction, giving a sensation of coldness.

26. What is the significance of bond energies in determining whether a reaction is endothermic?

Bond energies are crucial in determining whether a reaction is endothermic. If the total energy required to break bonds in the reactants is greater than the energy released when forming new bonds in the products, the reaction is endothermic. Understanding bond energies helps predict the overall energy change in a reaction.

27. How do endothermic reactions affect the kinetic energy of particles in a system?

Endothermic reactions increase the kinetic energy of particles within the reacting system. As heat is absorbed from the surroundings, this energy is converted into increased motion (kinetic energy) of the product molecules, often resulting in a more disordered system.

28. How do endothermic reactions relate to the concept of 'heat capacity'?

Heat capacity is the amount of heat required to raise the temperature of a substance by one degree. In endothermic reactions, the heat absorbed from the surroundings is related to the heat capacities of the reactants and products. Substances with higher heat capacities can absorb more heat with less temperature change.

29. Can you describe how endothermic reactions are represented in chemical equations?

In chemical equations, endothermic reactions are often represented with a heat term (ΔH) on the product side of the equation. For example:

30. What role do endothermic reactions play in phase changes?

Many phase changes, such as melting and vaporization, are endothermic processes. They require energy input to overcome intermolecular forces and increase the disorder of the system. For example, the melting of ice or the boiling of water are endothermic phase changes.

31. What is an endothermic reaction?

An endothermic reaction is a chemical process that absorbs heat energy from its surroundings. During this reaction, the system takes in more energy than it releases, resulting in a net increase in the system's energy and a decrease in the surrounding temperature.

32. What is the importance of endothermic reactions in biological systems?

Endothermic reactions are crucial in biological systems. For example:

33. How do endothermic reactions contribute to energy storage in chemical systems?

Endothermic reactions can store energy by converting thermal energy into chemical potential energy. This stored energy can later be released through exothermic reactions. This principle is used in rechargeable batteries, where electrical energy is stored through endothermic chemical reactions during charging.

34. What is the relationship between endothermic reactions and the concept of 'work' in thermodynamics?

In thermodynamics, work is energy transferred between a system and its surroundings. In endothermic reactions, the system often performs work on the surroundings (e.g., expansion work in gas-producing reactions). This work, along with heat absorption, contributes to the overall energy change of the system.

35. How do endothermic reactions affect the stability of chemical bonds?

Endothermic reactions often involve the formation of less stable chemical bonds compared to the bonds in the reactants. The energy absorbed during the reaction is used to form these higher-energy, less stable bonds in the products, which can store chemical potential energy.

36. What is the relationship between endothermic reactions and chemical equilibrium?

In a system at chemical equilibrium involving an endothermic reaction, adding heat (increasing temperature) will shift the equilibrium towards the products, favoring the endothermic direction. Conversely, removing heat will shift the equilibrium towards the reactants, as per Le Chatelier's Principle.

37. What is the significance of activation energy in endothermic reactions?

Activation energy in endothermic reactions is the minimum energy required for the reaction to proceed. It represents an energy barrier that reactants must overcome. In endothermic reactions, the activation energy is typically higher than in exothermic reactions, which is why many endothermic reactions require continuous energy input to proceed.

38. How does the concept of Gibbs free energy relate to endothermic reactions?

For an endothermic reaction to be spontaneous, the Gibbs free energy change (ΔG) must be negative. While the enthalpy change (ΔH) is positive for endothermic reactions, a sufficiently large increase in entropy (ΔS) can make ΔG negative, allowing the reaction to occur spontaneously.

39. What is the role of catalysts in endothermic reactions?

Catalysts lower the activation energy of a reaction without being consumed. In endothermic reactions, catalysts can help the reaction proceed more quickly or at lower temperatures by providing an alternative reaction pathway with lower activation energy, but they do not change the overall energy change of the reaction.

40. How does the rate of an endothermic reaction change with temperature?

Generally, increasing the temperature increases the rate of an endothermic reaction. Higher temperatures provide more kinetic energy to the reactant molecules, increasing the frequency and energy of collisions. This helps more molecules overcome the activation energy barrier, speeding up the reaction.

41. How does the entropy change in most endothermic reactions?

In most endothermic reactions, the entropy of the system increases. This is often due to an increase in the number of particles or greater molecular disorder in the products compared to the reactants. The increase in entropy can help make endothermic reactions spontaneous, especially at higher temperatures.

42. How can you experimentally determine if a reaction is endothermic?

To determine if a reaction is endothermic experimentally, you can:

43. What is the role of endothermic reactions in the design of chemical reactors?

In chemical reactor design, understanding endothermic reactions is crucial for:

44. How do endothermic reactions affect the concept of 'reversibility' in chemical processes?

Endothermic reactions are often more easily reversible than exothermic ones. This is because:

45. Can you describe how endothermic reactions are utilized in energy storage technologies?

Endothermic reactions are used in various energy storage technologies:

46. What is the importance of understanding endothermic reactions in the field of geochemistry?

In geochemistry, understanding endothermic reactions is crucial for:

47. How do endothermic reactions contribute to the concept of 'chemical weathering' in geology?

Endothermic reactions play a role in chemical weathering by: