What Are Reversible Reactions? | Reactions | Chemistry | FuseSchool

FuseSchool - Global Education

17 May 201302:45

Summary

TLDRThis educational lesson delves into the concept of reversible reactions, contrasting them with irreversible ones like frying an egg. It explains that reversible reactions allow products to revert to their original reactants, using the thermal decomposition of ammonium chloride into ammonia and hydrogen chloride as a demonstrative example. The experiment involves heating ammonium chloride in a fume cupboard, where the gases produced turn litmus paper blue and red, indicating their presence. Upon cooling, the gases recombine to form white ammonium chloride crystals, illustrating the reversibility of the reaction. The lesson also clarifies why this decomposition is not a 'sublimation reaction,' emphasizing the importance of distinguishing between phase changes and chemical reactions.

Takeaways

🍳 Reversible reactions are those where the products can revert to their original reactants, unlike irreversible reactions like frying an egg.
🔄 The reaction arrow is used to represent reversibility, indicating that the reaction can proceed in both forward and reverse directions.
🌡 An example of a reversible reaction is the thermal decomposition of ammonium chloride to form ammonia and hydrogen chloride, which can recombine to form ammonium chloride again.
🔬 Conducting the decomposition of ammonium chloride should be done in a fume cupboard due to the corrosive nature of the gases produced.
📝 Red litmus paper turns blue in the presence of ammonia, and blue litmus paper turns red in the presence of hydrogen chloride, confirming the products of the reaction.
🔬 Upon cooling the boiling tube, white crystals of ammonium chloride reappear, demonstrating the reversibility of the reaction.
🧪 Ammonium chloride decomposes into ammonia and hydrogen chloride when heated, and these gases can react to reform ammonium chloride upon cooling.
🚫 The term 'sublimation reaction' is incorrect for the thermal decomposition of ammonium chloride because sublimation refers to a phase change, not a chemical reaction.
🌡 During sublimation, a solid turns directly into a gas without becoming a liquid, which is different from the decomposition process that forms new substances.
🔍 Solid ammonium chloride does not form gaseous ammonium chloride but decomposes into ammonia and hydrogen chloride, highlighting the difference between sublimation and decomposition.
📚 Understanding the distinction between reversible reactions, sublimation, and decomposition is crucial for correctly interpreting chemical processes.

Q & A

What is a reversible reaction?
-A reversible reaction is a type of chemical reaction where the products can revert or go back to their original reactants, meaning the reaction can proceed in both the forward and reverse directions.
Why is it impossible to 'unfry' an egg?
-It is impossible to 'unfry' an egg because the process of frying an egg is an irreversible reaction. Once the proteins in the egg have been denatured and the egg has been cooked, the reaction cannot be reversed to return the egg to its uncooked state.
What is an example of an irreversible reaction mentioned in the script?
-The combustion of magnesium to form magnesium oxide is an example of an irreversible reaction mentioned in the script.
What symbol represents reversibility in a chemical reaction?
-A reaction arrow with a double-headed arrow (⇌) is used to represent reversibility in a chemical reaction.
What is the thermal decomposition of ammonium chloride?
-The thermal decomposition of ammonium chloride is a reversible reaction where ammonium chloride decomposes into ammonia and hydrogen chloride when heated.
Why should the thermal decomposition of ammonium chloride be conducted in a fume cupboard?
-The thermal decomposition of ammonium chloride should be conducted in a fume cupboard because both ammonia and hydrogen chloride are corrosive gases, and the fume cupboard helps to contain and vent these gases safely.
How can you confirm the presence of ammonia in the reaction?
-The presence of ammonia can be confirmed by holding red litmus paper at the mouth of the boiling tube; if the paper turns blue, it indicates the presence of ammonia.
How can you confirm the presence of hydrogen chloride in the reaction?
-The presence of hydrogen chloride can be confirmed by using blue litmus paper; if the paper turns red, it indicates the presence of hydrogen chloride.
What do you observe near the mouth of the boiling tube after cooling?
-After removing the boiling tube from the heat and allowing it to cool, you will observe white crystals near the mouth of the tube, which are ammonium chloride crystals.
Why is the thermal decomposition of ammonium chloride sometimes incorrectly called a 'sublimation reaction'?
-The thermal decomposition of ammonium chloride is sometimes incorrectly called a 'sublimation reaction' because it involves a phase change from solid to gas. However, it is not a sublimation reaction because the substance itself changes into different products (ammonia and hydrogen chloride) rather than simply transitioning from solid to gas.
What is the balanced chemical equation for the reversible reaction of ammonium chloride?
-The balanced chemical equation for the reversible reaction of ammonium chloride is NH4Cl(s) → NH3(g) + HCl(g), with the reverse reaction being NH3(g) + HCl(g) → NH4Cl(s).

Outlines

00:00

🔁 Reversible Reactions and the Example of Ammonium Chloride

This paragraph introduces the concept of reversible reactions, contrasting them with irreversible processes like frying an egg. It defines reversible reactions as those where products can revert to their original reactants, using the thermal decomposition of ammonium chloride as a key example. The process involves heating ammonium chloride in a boiling tube under a fume cupboard, which decomposes into ammonia and hydrogen chloride gases. The presence of these gases is confirmed using red and blue litmus paper, which turn blue and red respectively. Upon cooling, the gases recombine to form white ammonium chloride crystals, demonstrating the reversibility of the reaction. The paragraph also clarifies a common misconception by explaining why the thermal decomposition of ammonium chloride is not a 'sublimation reaction', emphasizing that sublimation is a phase change, not a chemical reaction.

Mindmap

Keywords

💡Reversible Reactions

Reversible reactions are chemical processes where the products can be converted back into the original reactants under certain conditions. This concept is central to the video's theme as it highlights the dynamic nature of some chemical reactions. In the script, the thermal decomposition of ammonium chloride to form ammonia and hydrogen chloride, and their subsequent recombination to form ammonium chloride again, exemplifies a reversible reaction.

💡Irreversible Reactions

Irreversible reactions are those that cannot be reversed under normal conditions, meaning they proceed in one direction only. The video uses the example of frying an egg to illustrate this concept, emphasizing that once an egg is fried, it cannot be 'unfried'. This serves as a contrast to reversible reactions, which is a key point in understanding the different types of chemical reactions.

💡Combustion

Combustion is a chemical reaction that occurs between a substance and an oxidant, typically producing heat and light. In the script, the combustion of magnesium to form magnesium oxide is mentioned as an example of an irreversible reaction. This process is relevant to the video's theme as it demonstrates a common type of reaction that is not reversible.

💡Thermal Decomposition

Thermal decomposition is a chemical reaction where a compound breaks down into two or more simpler substances when heated. The video script specifically discusses the thermal decomposition of ammonium chloride, which breaks down into ammonia and hydrogen chloride. This process is a key example of a reversible reaction in the video.

💡Ammonium Chloride

Ammonium chloride is a chemical compound that serves as a reactant in the reversible reaction discussed in the video. It decomposes into ammonia and hydrogen chloride when heated, and these products can recombine to form ammonium chloride again when cooled. The script uses this compound to demonstrate the concept of reversibility in chemical reactions.

💡Ammonia

Ammonia is a compound with the formula NH3, which is a product of the thermal decomposition of ammonium chloride. In the video, the presence of ammonia is confirmed by its reaction with red litmus paper, turning it blue. This serves as a practical demonstration of how products of a reversible reaction can be identified.

💡Hydrogen Chloride

Hydrogen chloride, with the chemical formula HCl, is another product of the thermal decomposition of ammonium chloride. The script describes how blue litmus paper turns red in the presence of hydrogen chloride, confirming its formation as part of the reversible reaction process.

💡Bunsen Burner

A Bunsen burner is a type of laboratory burner used to produce a single flat flame. In the context of the video, it is used to heat ammonium chloride in a boiling tube, facilitating its thermal decomposition. The Bunsen burner is an essential tool in demonstrating the reversible reaction in the video.

💡Fume Cupboard

A fume cupboard is a laboratory safety device that captures and exhausts fumes generated from experiments. The script mentions conducting the experiment in a fume cupboard due to the corrosive nature of ammonia and hydrogen chloride. This highlights the importance of safety precautions in chemical experiments.

💡Sublimation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. The video script clarifies that the thermal decomposition of ammonium chloride is sometimes incorrectly referred to as a 'sublimation reaction', but this is a misnomer because sublimation does not involve a chemical reaction, whereas the decomposition does.

💡Litmus Paper

Litmus paper is a type of paper that is used to test the acidity or alkalinity of substances. In the video, red and blue litmus papers are used to confirm the presence of ammonia and hydrogen chloride, respectively. This demonstrates a practical application of litmus paper in identifying products of a reversible chemical reaction.

Highlights

Lesson on reversible reactions and their characteristics.

Comparison of irreversible reactions like frying an egg to reversible ones.

Introduction to the concept of reversibility in chemical reactions.

Use of a reversible reaction arrow to denote reactions that can proceed in both directions.

Example of a reversible reaction: thermal decomposition of ammonium chloride.

Demonstration of the experiment involving ammonium chloride, ammonia, and hydrogen chloride.

Safety precautions when conducting experiments with corrosive gases.

Confirmation of ammonia presence using red litmus paper.

Confirmation of hydrogen chloride presence using blue litmus paper.

Observation of ammonium chloride crystals forming upon cooling the reaction.

Explanation of the reversible process of ammonium chloride decomposing and reforming.

Clarification of the chemical equation for the reversible reaction.

Discussion on why the thermal decomposition of ammonium chloride is not a 'sublimation reaction'.

Explanation of phase changes and the distinction between sublimation and a chemical reaction.

Clarification that solid ammonium chloride decomposes into ammonia and hydrogen chloride, not sublimates.

Emphasis on the importance of understanding the difference between phase changes and chemical reactions.