Exothermic Reactions
Exothermic reactions are reactions or processes that emit energy, usually in the form of heat or light.
In an exothermic reaction, energy is released since the overall energy of the products is less than the overall energy of the reactants.
For this reason, the change in enthalpy, ΔH, for an exothermic reaction will constantly be negative. In the presence of water, a strong acid will dissociate quickly and release heat, so it is an exothermic reaction.
Numerous chain reactions emit or release energy in the form of heat, light, or sound.
Exothermic reactions may take place spontaneously and lead to higher randomness or entropy (ΔS > 0) of the system. In the laboratory, exothermic reactions produce heat or may even be explosive.
- 1) Endothermic Reactions
- 2) Reaction progression
- 3) Examples of Endothermic and Exothermic Processes
- 4) Exothermic Reactions
- 5) Endergonic and Exergonic Reactions
- 6) MCQs: Exothermic and Endothermic Reactions
- 7) FAQs: Exothermic and Endothermic Reactions
- 8) Summary of Exothermic and Endothermic Reactions Tutorial
- 9) You may also like to learn:
Endothermic Reactions
Endothermic reactions are reactions that need external energy, typically in the form of heat, for the reaction to proceed. Considering that endothermic reactions attract heat from their environments, they tend to cause their environments to cool off.
They are also normally non-spontaneous, given that endothermic reactions yield products that are greater in energy than the reactants. As such, the change in enthalpy for an endothermic reaction is constantly positive. In order to melt the ice cube, heat is needed, so the procedure is endothermic.
Endothermic reactions can not take place spontaneously. Work needs to be done in order to get these reactions to take place.
Reaction progression
Exothermic reaction
In an exothermic reaction, the overall energy of the products is less than the total energy of the reactants. For that reason, the change in enthalpy is negative, and heat is released to the surroundings.
Endothermic reaction
In an endothermic reaction, the products are higher in energy than the reactants. For that reason, the change in enthalpy is positive, and heat is taken in from the environments by the reaction.
Examples of Endothermic and Exothermic Processes
Endothermic Reactions
Photosynthesis is an example of an endothermic chain reaction. In this process, plants utilize the energy from the sun to transform CO2 and water into glucose and oxygen. This reaction requires 15MJ of energy (sunshine) for every single kg of glucose that is produced:
sunlight + 6CO2(g) + WATER(l) = C6H12O6(aq) + 6O2(g)
Other examples of endothermic processes include:
- Dissolving ammonium chloride in water.
- Breaking alkanes.
- Nucleosynthesis of elements heavier than a nickel in stars.
- Evaporating liquid water.
- Melting ice.
Exothermic Reactions
An example of an exothermic reaction is the mixture of salt and chlorine to yield table salt. This reaction produces 411 kJ of energy for each mole of salt that is produced:
Na(s) + 0.5 Cl2(s) = NaCl(s)
Other examples of exothermic procedures consist of:
- The thermite reaction.
- A neutralization reaction (e.g., mixing an acid and a base to form a salt and water).
- Many polymerization reactions.
- Combustion of a fuel.
- Nuclear fission.
Endergonic and Exergonic Reactions
Endothermic and exothermic reactions refer to the absorption or release of heat. There are other kinds of energy that may be produced or soaked up by a chain reaction. Examples include light and noise. In general, reactions involving energy might be categorized as endergonic or exergonic.
An endothermic reaction is an example of an endergonic reaction. An exothermic reaction is an example of an exergonic reaction.
Difference Between Endothermic and Exothermic Reactions
| Endothermic Reaction | Exothermic Reaction |
| A reaction in which the system absorbs energy from its surrounding in the form of heat. | A reaction in which energy is released from the system in the form of heat. |
| The energy is absorbed from the surrounding environment into the reaction. | The energy is released from the system to its surrounding environment. |
| Energy remains in the form of heat. | Energy is emitted as heat, electricity, light, or sound. |
| Melting ice, evaporation, cooking, gas molecules, photosynthesis is a few examples. | Rusting iron, settling, chemical bonds, surges, nuclear fission are a few examples. |
MCQs: Exothermic and Endothermic Reactions
- What characterizes an exothermic reaction?
- a) Absorption of heat
- b) Release of energy, usually as heat or light
- c) Requirement of external energy
- d) Cooling of the surroundings
Answer: b
- What is the overall energy change in an exothermic reaction?
- a) Positive
- b) Negative
- c) Zero
- d) Variable
Answer: b
- In an endothermic reaction, what happens to the surroundings?
- a) They cool off
- b) They heat up
- c) No change
- d) Become explosive
Answer: a
- What does the change in enthalpy (ΔH) signify for an endothermic reaction?
- a) Always negative
- b) Always positive
- c) Variable
- d) Depends on the specific reaction
Answer: b
- Which of the following reactions is considered non-spontaneous?
- a) Exothermic reaction
- b) Endothermic reaction
- c) Both
- d) Neither
Answer: b
- What is the key characteristic of an endothermic reaction?
- a) Energy release
- b) Low randomness
- c) External energy requirement
- d) Spontaneity
Answer: c
- In an exothermic reaction, what happens to the enthalpy?
- a) Decreases
- b) Increases
- c) Stays constant
- d) Becomes unpredictable
Answer: a
- Which process is an example of an endothermic reaction?
- a) Combustion
- b) Photosynthesis
- c) Neutralization
- d) Polymerization
Answer: b
- What is the primary form of energy released in exothermic reactions?
- a) Light
- b) Sound
- c) Heat
- d) Electricity
Answer: c
- Which reaction involves the absorption of sunlight to produce glucose and oxygen?
- a) Combustion
- b) Dissolution
- c) Photosynthesis
- d) Neutralization
Answer: c
- What type of reaction is the dissolution of ammonium chloride in water?
- a) Exothermic
- b) Endothermic
- c) Neutral
- d) Spontaneous
Answer: b
- In an exothermic reaction, what happens to the products’ energy compared to the reactants?
- a) Increases
- b) Decreases
- c) Remains the same
- d) Becomes unpredictable
Answer: b
- Which reaction produces table salt and is exothermic?
- a) Polymerization
- b) Photosynthesis
- c) Neutralization
- d) Evaporation
Answer: c
- What characterizes an endergonic reaction?
- a) Release of energy
- b) Absorption of heat
- c) Non-spontaneous
- d) Low entropy
Answer: b
- What is an example of an exergonic reaction?
- a) Melting ice
- b) Evaporation
- c) Rusting iron
- d) Dissolution
Answer: c
- Which of the following is a difference between endothermic and exothermic reactions?
- a) Both absorb heat
- b) Both release heat
- c) One absorbs, and one releases heat
- d) Neither absorbs nor releases heat
Answer: c
- What is the energy form emitted in an exothermic reaction?
- a) Heat
- b) Light
- c) Both a and b
- d) Neither a nor b
Answer: c
- Which reaction involves the absorption of heat to melt ice?
- a) Exothermic
- b) Photosynthesis
- c) Endothermic
- d) Combustion
Answer: c
- What type of reaction is the combustion of a fuel?
- a) Endothermic
- b) Exothermic
- c) Neutral
- d) Explosive
Answer: b
FAQs: Exothermic and Endothermic Reactions
- What are exothermic reactions?
- Exothermic reactions are processes that release energy, typically in the form of heat or light. In these reactions, the overall energy of the products is less than the overall energy of the reactants.
- How is enthalpy change (ΔH) related to exothermic reactions?
- In exothermic reactions, ΔH is always negative, indicating a release of energy. For example, the dissociation of a strong acid in water is an exothermic reaction.
- Can exothermic reactions occur spontaneously?
- Yes, exothermic reactions can take place spontaneously and often lead to increased randomness or entropy in the system.
- Give examples of exothermic processes in the laboratory.
- Exothermic reactions in the laboratory may produce heat or be explosive. Examples include combustion reactions, neutralization reactions, and the thermite reaction.
- What characterizes endothermic reactions?
- Endothermic reactions require external energy, usually in the form of heat, for the reaction to proceed. These reactions absorb heat from their surroundings, causing a cooling effect.
- Is the change in enthalpy (ΔH) positive or negative for endothermic reactions?
- The change in enthalpy for endothermic reactions is always positive, indicating an absorption of energy. For instance, melting ice requires heat and is an endothermic process.
- Can endothermic reactions occur spontaneously?
- Endothermic reactions cannot occur spontaneously; external work or energy input is needed to make them happen.
- Provide examples of endothermic processes.
- Examples of endothermic processes include photosynthesis (sunlight converting CO2 and water into glucose and oxygen), dissolving ammonium chloride in water, and the melting of ice.
- What is the key difference between exothermic and endothermic reactions in terms of enthalpy change?
- In an exothermic reaction, the enthalpy change is negative, indicating a release of energy, while in an endothermic reaction, the enthalpy change is positive, indicating an absorption of energy.
- How does the progression of exothermic reactions differ from endothermic reactions?
- In an exothermic reaction, the overall energy of the products is less than that of the reactants, resulting in a negative change in enthalpy and the release of heat. In an endothermic reaction, the products have higher energy, leading to a positive change in enthalpy and heat absorption.
- Give examples of exothermic reactions.
- Examples of exothermic reactions include the formation of table salt (NaCl) from the mixture of sodium and chlorine, combustion of fuels, and various polymerization reactions.
- What are endergonic and exergonic reactions?
- Endergonic reactions require an input of energy, while exergonic reactions release energy. Both endothermic and exothermic reactions fall under these categories, depending on whether energy is absorbed or released.
- How can one differentiate between endothermic and exothermic reactions?
- Endothermic reactions absorb energy from the surroundings, resulting in a positive change in enthalpy, while exothermic reactions release energy to the surroundings, causing a negative change in enthalpy.
- Give practical examples illustrating the difference between endothermic and exothermic reactions.
- Melting ice, evaporation, and photosynthesis are examples of endothermic reactions, absorbing energy. Rusting iron, combustion, and nuclear fission are examples of exothermic reactions, releasing energy.
- What forms of energy can be emitted in exothermic reactions?
- Exothermic reactions can emit energy in the form of heat, electricity, light, or sound.
- Are endothermic reactions spontaneous?
- No, endothermic reactions are non-spontaneous and require external work or energy input to occur.
- How are endothermic reactions significant in daily life or industry?
- Endothermic reactions, such as photosynthesis, play a crucial role in processes like energy conversion in plants and are essential for various industrial applications.
Summary of Exothermic and Endothermic Reactions Tutorial
In this comprehensive tutorial, we explored the fascinating world of exothermic and endothermic reactions, uncovering their definitions, examples, and key differences. Let’s recap the essential points covered:
- Exothermic Reactions:
- These reactions release energy, often in the form of heat or light. The overall energy of the products is lower than that of the reactants, resulting in a negative change in enthalpy (ΔH). Examples include the spontaneous dissociation of strong acids and explosive laboratory reactions.
- Endothermic Reactions:
- Requiring external energy, typically in the form of heat, endothermic reactions absorb energy from their surroundings. The products have higher energy than the reactants, leading to a positive ΔH. Endothermic processes, such as photosynthesis and melting ice, are non-spontaneous and require external work.
- Reaction Progression:
- In an exothermic reaction, the products have lower energy, causing a negative ΔH, and heat is released to the surroundings. Conversely, in an endothermic reaction, the products are higher in energy, resulting in a positive ΔH, and heat is absorbed from the surroundings.
- Examples of Endothermic and Exothermic Processes:
- Endothermic Reactions: Photosynthesis, dissolving ammonium chloride, breaking alkanes, nucleosynthesis in stars, evaporating liquid water, and melting ice.
- Exothermic Reactions: Formation of table salt, thermite reaction, neutralization reactions, polymerization reactions, combustion of fuel, and nuclear fission.
- Endergonic and Exergonic Reactions:
- These terms refer to the absorption or release of heat, where endergonic reactions absorb energy, and exergonic reactions release energy. Endothermic and exothermic reactions serve as examples of endergonic and exergonic processes, respectively.
- Difference Between Endothermic and Exothermic Reactions:
-
Endothermic Reaction Exothermic Reaction Absorbs energy from surroundings Releases energy from the system Energy is absorbed from the environment into the reaction Energy is released from the system to its surroundings Energy remains in the form of heat Energy is emitted as heat, electricity, light, or sound Examples: Melting ice, evaporation, photosynthesis Examples: Rusting iron, settling, combustion, nuclear fission
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This tutorial equips you with a deep understanding of the thermodynamics behind these reactions, their real-world applications, and their significance in various fields. Whether you’re delving into chemistry, thermodynamics, or industrial processes, this knowledge provides a foundation for predicting, controlling, and optimizing reactions and processes.