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Exothermic Reaction - Meaning, Definition, Examples, Causes, FAQs

Exothermic Reaction - Meaning, Definition, Examples, Causes, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:33 PM IST

Define Exothermic reaction.

Exothermic Definition: Exothermic meaning is a chemical reaction that involves the release of energy in the form of heat or light is known as an exothermic process. These reactions are the opposites of endothermic reactions, and they can be written as follows in a chemical equation: Products + Reactants + Energy. As a result, it's easy to see how the net amount of energy required to start an exothermic process is less than the net amount of energy released.

This Story also Contains
  1. Define Exothermic reaction.
  2. Exothermic Reaction Examples
  3. Combustion
  4. Detonation of Nitroglycerin
  5. Nuclear Fission of Uranium-235
  6. Neutralization Reactions
  7. What Causes Respiration to be an Exothermic Process?

The net quantity of heat energy that passes through a calorimeter, an instrument used to quantify the heat released by a chemical reaction, is equal to the negative of the total energy change of the system. However, measuring or even calculating the absolute total of energy in a chemical system is extremely challenging. As a result, the energy change (also known as the enthalpy change and indicated by the letter H) is measured instead. The following equation describes the relationship between the value of H and the reaction's bond energies.

ΔH = (energy used in the creation of bonds that result in products) - (energy released when the reactant bonds are broken)

As a result, it is clear that the change in enthalpy for an exothermic reaction will always be negative, i.e. ΔH < 0.

Bomb calorimeters are excellent tools for determining the enthalpy change of combustion reactions.

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Exothermic Reaction Examples

The following are some instances of exothermic examples that occur in everyday life:

  1. Exploding a firecracker — one of the greatest illustrations of an exothermic reaction is the bursting of a firecracker, which produces a loud bang as well as light and heat.

  2. Lighting a candle - this is a continual reaction in which the wax works as fuel and burns for a long time.

  3. When you turn on a light bulb, the electric current induces a reaction in the tungsten filament, which produces light and heat.

  4. Fuel combustion - whether in a car engine or a gas stove, fuel combustion is an exothermic reaction. The heat created is utilized for a variety of reasons, including operating a motor, cooking, and so on.

  5. When hydrogen is used in hydrogen-oxygen fuel cells, it undergoes combustion and produces an electric charge, which is an exothermic reaction.

  6. Another example of an exothermic reaction is the combustion of natural gas methane. Exothermic reaction examples equations:

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CH₄+2O₂→CO₂+2H₂O

Many more examples of this type of reaction can be found in the environment. The trick is to determine if these processes emit energy into the environment in the form of light, heat, or, in certain situations, sound. Acid and alkali neutralization reactions, water and reactive metals, and weakly reactive metals with strong acids are some of the more advanced varieties of such reactions. Self-heating technology also makes advantage of exothermic reactions.

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Combustion

Combustion is the process of burning in which a fuel undergoes reduction and oxidation in order to release energy in some form. Combustion is demonstrated by lighting undesirable papers with kerosene and a matchstick. To put it another way, combustion is anything that burns and releases energy. As oxygen is such an important element in burning, it plays an important role as an oxidizing agent in most types of combustion.

It does, however, produce dangerous by-products such as smoke and ash. By-products like these are one of the most common sources of air pollution. Farmers' stubble burning in various northern Indian states in late 2019 resulted in substantial amounts of smog (a mixture of smoke and fog). This had a negative impact on the state of New Delhi's atmosphere, causing its air quality to plummet to dangerously low levels.

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Detonation of Nitroglycerin

Nitroglycerin is a flammable chemical that is commonly used in the manufacture of explosives. Its highly flammable physical qualities, which allow it to catch fire quickly and easily, make it a desirable component for explosives and dynamite. For combustion, it is frequently combined with another fuel. When nitroglycerin is detonated, it causes the surrounding fuel to burn, resulting in a shockwave that can travel at 30 times the speed of sound.

The detonation itself is an exothermic process since it produces a large amount of gases and a very high temperature (upwards of 5,000 degrees Celsius). The physical properties of nitroglycerin allow it to disintegrate and release huge amounts of energy during combustion. It's for this reason that it's the favored chemical in high-explosive devices.

Nuclear Fission of Uranium-235

Uranium-235 fission is another example of an exothermic process. Fission releases energy in the form of heat and gamma rays when it occurs. This energy can be used in a variety of businesses. The reaction also produces nuclei and neutrons, which must be appropriately eliminated to avoid contamination of the environment. Uranium nuclear fission is a high-profile reaction that must be carried out in carefully regulated conditions.

It is also one of the most efficient ways of disseminating energy, producing 2.5 million times the energy produced by coal combustion, which is one of the most popular varieties nowadays.

NCERT Chemistry Notes:

Neutralization Reactions

These are reactions in which both acidic and basic components are involved in the combustion. As a result, by-products such as salt and water are formed. Neutralization reactions are named such because they neutralize the pH of the interacting components.

What Causes Respiration to be an Exothermic Process?

The process through which people take in oxygen and exhale carbon dioxide is known as respiration. The following is the chemical equation for this procedure:

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

It's worth noting that C6H12O6 is the formula for glucose, which mixes with the oxygen inhaled by humans to produce carbon dioxide, water, and energy. As of the energy released during the reaction, respiration is an exothermic reaction.

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Frequently Asked Questions (FAQs)

1. 1.In an exothermic reaction, does the temperature rise?

The temperature of the reaction mixture rises as energy is released in an exothermic process. The temperature drops when energy is absorbed in an endothermic reaction.

2. 2.What are the products of exothermic reactions?

Exothermic reactions are those in which energy is released, usually in the form of heat or light. As total energy of products is less than total energy of reactants, energy is released in an exothermic reaction.

3. 3.How does the temperature of an exothermic reaction impact it?

Heat is a result of an exothermic process. As a result, raising the temperature causes the equilibrium to shift to the left, while lowering the temperature causes the equilibrium to shift to the right.

4. 4.What are the signs that a reaction is exothermic?

 An exothermic reaction, which releases heat into the environment, has a negative ΔH by convention, because enthalpy of products is lower than enthalpy of system's reactants. These reactions have enthalpies that are less than zero, making them exothermic.

5. 5.Give two exothermic reactions as examples.

The following are some instances of exothermic reactions that occur in everyday life: Bursting a firecracker - one of the greatest illustrations of an exothermic reaction is the bursting of a firecracker, which produces a loud bang as well as light and heat. Lighting a candle is a continual reaction in which the wax works as a fuel and produces a flame that lasts for a long time.

6. How do exothermic reactions contribute to climate change?
Many exothermic reactions, particularly combustion reactions involving fossil fuels, release greenhouse gases like carbon dioxide into the atmosphere. These gases trap heat in the Earth's atmosphere, contributing to global warming and climate change. Understanding and managing these reactions is crucial for addressing environmental concerns.
7. What is the role of exothermic reactions in the development of renewable energy technologies?
Exothermic reactions are crucial in renewable energy technologies:
8. How do exothermic reactions contribute to the study of reaction mechanisms?
Exothermic reactions provide valuable insights into reaction mechanisms:
9. How do exothermic reactions impact the environment on a global scale?
Exothermic reactions have significant environmental impacts:
10. How do exothermic reactions relate to the concept of chemical stability?
Exothermic reactions often lead to the formation of more stable chemical species. The release of energy indicates that the products are in a lower energy state than the reactants, which generally correlates with increased stability. This concept is fundamental to understanding molecular stability and reactivity in chemistry.
11. What is an exothermic reaction?
An exothermic reaction is a chemical process that releases energy to its surroundings in the form of heat. During this reaction, the system loses energy, causing the temperature of the surrounding environment to increase.
12. How does an exothermic reaction affect the temperature of its surroundings?
An exothermic reaction increases the temperature of its surroundings. As the reaction releases heat energy, this energy is transferred to the surrounding environment, causing it to warm up.
13. How is enthalpy change (ΔH) represented in an exothermic reaction?
In an exothermic reaction, the enthalpy change (ΔH) is negative. This negative value indicates that energy is released from the system to the surroundings during the reaction.
14. How does bond breaking and formation relate to exothermic reactions?
In exothermic reactions, the energy released from forming new bonds is greater than the energy required to break existing bonds. This net release of energy is what makes the reaction exothermic. The stronger the new bonds formed compared to the bonds broken, the more exothermic the reaction.
15. What is the difference between exothermic and endothermic reactions?
The main difference is the direction of heat flow. Exothermic reactions release heat to the surroundings, while endothermic reactions absorb heat from the surroundings. Exothermic reactions result in a temperature increase of the surroundings, while endothermic reactions cause a temperature decrease.
16. How do exothermic reactions affect reaction rates?
Exothermic reactions can accelerate as they progress because the heat released can provide additional energy to overcome the activation energy barrier for subsequent reactions. This can lead to a phenomenon known as thermal runaway in some cases, where the reaction rate increases dramatically due to the heat produced.
17. How do exothermic reactions contribute to the study of chemical thermodynamics?
Exothermic reactions are central to the study of chemical thermodynamics:
18. How do exothermic reactions contribute to the concept of chemical potential energy?
Exothermic reactions release chemical potential energy stored in molecular bonds. As the reaction proceeds, this potential energy is converted into kinetic energy (heat). The difference in chemical potential energy between reactants and products determines the amount of heat released in an exothermic reaction.
19. What is the significance of exothermic reactions in the field of nanotechnology?
In nanotechnology, exothermic reactions are important for:
20. How do exothermic reactions relate to the concept of chemical kinetics?
Exothermic reactions influence chemical kinetics in several ways:
21. Can you provide some everyday examples of exothermic reactions?
Common examples of exothermic reactions include:
22. What is the role of exothermic reactions in chemical hand warmers?
Chemical hand warmers typically use exothermic reactions to generate heat. Common types use the oxidation of iron powder, which is an exothermic process. When exposed to air, the iron reacts with oxygen, releasing heat that warms the surrounding material and, consequently, the user's hands.
23. Can an exothermic reaction occur at low temperatures?
Yes, exothermic reactions can occur at low temperatures. The exothermic nature of a reaction is determined by the energy difference between reactants and products, not by the initial temperature. Some exothermic reactions, like certain crystallization processes, can even release heat while occurring in very cold environments.
24. What is the connection between exothermic reactions and chemical energy storage?
Exothermic reactions are often used in chemical energy storage systems. Energy can be stored by creating chemical bonds that release energy when broken. For example, batteries store energy in chemical form and release it through exothermic redox reactions. Understanding these processes is crucial for developing efficient energy storage technologies.
25. What is the importance of understanding exothermic reactions in the field of materials engineering?
Understanding exothermic reactions is crucial in materials engineering for:
26. How can you experimentally determine if a reaction is exothermic?
To determine if a reaction is exothermic, you can:
27. How do exothermic reactions relate to bond energies?
In exothermic reactions, the total bond energy of the products is lower than the total bond energy of the reactants. This difference in bond energy is released as heat to the surroundings. The more stable the bonds formed in the products compared to those in the reactants, the more exothermic the reaction will be.
28. How do exothermic reactions contribute to the formation of chemical bonds?
Exothermic reactions often involve the formation of stronger or more stable chemical bonds. The energy released during an exothermic reaction is a result of electrons settling into lower energy states as new bonds form. This process is fundamental to understanding chemical bonding and molecular stability.
29. What is the difference between heat of reaction and heat of formation in exothermic processes?
Heat of reaction is the energy released or absorbed during a chemical reaction, while heat of formation is the energy change when one mole of a compound is formed from its elements in their standard states. For an exothermic reaction, both values are negative, but they measure different aspects of the energy change in a chemical process.
30. How do exothermic reactions relate to the concept of entropy?
Exothermic reactions generally increase the entropy of the surroundings by releasing heat energy. This aligns with the second law of thermodynamics, which states that the total entropy of an isolated system always increases. However, the entropy change of the system itself can be positive or negative in an exothermic reaction, depending on other factors like changes in the number of gas molecules.
31. What safety precautions should be taken when working with exothermic reactions?
When working with exothermic reactions, consider the following safety measures:
32. What is the significance of exothermic reactions in the field of materials science?
In materials science, exothermic reactions are important for:
33. What role do exothermic reactions play in the formation of chemical bonds in the universe?
Exothermic reactions are fundamental to the formation of chemical bonds throughout the universe. In stars, nuclear fusion reactions (which are exothermic) lead to the formation of heavier elements. These elements can then form chemical bonds through exothermic processes, contributing to the formation of molecules and compounds in space.
34. How do exothermic reactions influence the design of chemical reactors?
Exothermic reactions significantly impact chemical reactor design:
35. What is the relationship between exothermic reactions and the heat capacity of substances?
The heat capacity of substances involved in an exothermic reaction affects how the released energy manifests as a temperature change. Substances with higher heat capacities will show smaller temperature increases for the same amount of heat released, while those with lower heat capacities will exhibit larger temperature changes.
36. What role do exothermic reactions play in living organisms?
Exothermic reactions are crucial for living organisms. They provide the energy needed for various biological processes, such as metabolism, muscle contraction, and maintaining body temperature. For example, the breakdown of glucose during cellular respiration is an exothermic process that releases energy for cellular functions.
37. What is the significance of exothermic reactions in the field of chemistry?
Exothermic reactions are significant in chemistry for several reasons:
38. Why do exothermic reactions often occur spontaneously?
Exothermic reactions often occur spontaneously because they release energy, making them thermodynamically favorable. The release of energy increases the entropy of the surroundings, which aligns with the second law of thermodynamics.
39. What is the relationship between exothermic reactions and activation energy?
Exothermic reactions still require activation energy to initiate the reaction, even though they release energy overall. The activation energy is the initial energy barrier that reactants must overcome for the reaction to proceed. Once this barrier is surpassed, the reaction releases more energy than it consumed, resulting in a net exothermic process.
40. What is the relationship between exothermic reactions and chemical bonds?
In exothermic reactions, the formation of new chemical bonds releases more energy than is required to break the existing bonds. This net release of energy is what characterizes the reaction as exothermic. The strength and type of bonds broken and formed determine the amount of energy released.
41. How do catalysts affect exothermic reactions?
Catalysts lower the activation energy required for a reaction to occur, which can increase the rate of an exothermic reaction. However, catalysts do not change the overall energy released or the nature of the reaction (i.e., they don't make an endothermic reaction exothermic or vice versa).
42. How do exothermic reactions impact the equilibrium of a reversible reaction?
In a reversible reaction, an exothermic forward reaction implies an endothermic reverse reaction. According to Le Chatelier's principle, increasing the temperature will shift the equilibrium towards the endothermic direction (reverse reaction), while decreasing the temperature will favor the exothermic direction (forward reaction).
43. What is the role of exothermic reactions in the formation of chemical equilibrium?
Exothermic reactions influence chemical equilibrium by affecting the balance between forward and reverse reactions. As an exothermic reaction proceeds, it releases heat, which can shift the equilibrium according to Le Chatelier's principle. Understanding this relationship is crucial for predicting and controlling equilibrium conditions in chemical systems.
44. Can an exothermic reaction be reversed?
Yes, an exothermic reaction can be reversed, but the reverse reaction will be endothermic. The reverse process will require the same amount of energy that was released in the original exothermic reaction. This concept is related to Le Chatelier's principle in chemical equilibrium.
45. What is the connection between exothermic reactions and spontaneity?
Exothermic reactions are often spontaneous because they release energy, increasing the entropy of the surroundings. However, not all exothermic reactions are spontaneous, and not all spontaneous reactions are exothermic. The spontaneity of a reaction depends on both enthalpy change (ΔH) and entropy change (ΔS), as described by the Gibbs free energy equation.
46. How do exothermic reactions contribute to the concept of enthalpy in thermodynamics?
Exothermic reactions decrease the enthalpy of a system. The enthalpy change (ΔH) for an exothermic reaction is negative, indicating that the products have less energy than the reactants. This concept is fundamental to understanding energy flow in chemical processes and is a key component of thermodynamic calculations.
47. Can a reaction be both exothermic and endothermic?
A single reaction cannot be both exothermic and endothermic simultaneously. However, a complex process may involve multiple steps, some of which are exothermic and others endothermic. The overall nature of the process (exothermic or endothermic) depends on the net energy change across all steps.
48. What is the importance of exothermic reactions in the field of biochemistry?
In biochemistry, exothermic reactions are crucial for:
49. How do exothermic reactions relate to the concept of chemical potential?
Exothermic reactions involve a decrease in chemical potential from reactants to products. The chemical potential represents the potential energy stored in chemical bonds and molecular structures. In an exothermic reaction, this potential energy is released, leading to a lower chemical potential in the products compared to the reactants.
50. What role do exothermic reactions play in the field of green chemistry?
In green chemistry, understanding and optimizing exothermic reactions is important for:
51. How do exothermic reactions contribute to the concept of chemical affinity?
Exothermic reactions often indicate a high chemical affinity between reactants.

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