Question

The product formed when ethene and air under pressure is passed over silver catalyst heated to \(500 \mathrm{~K}\) is (a) Epoxy ethane (b) Ethanal (c) Ethanoic acid (d) Methanal

Short answer

Answer: Ethanal (b).

Step-by-step solution

Identify the reactants

In this reaction, the reactants are ethene (C2H4) and air, which mainly consists of oxygen. The catalyst used is silver, and the reaction occurs at a temperature of 500 K.

Recall and apply knowledge of ethene reactions

Ethene is an unsaturated hydrocarbon with a double bond. It can undergo a range of reactions, including addition, oxidation, and halogenation. In the presence of a catalyst and a suitable temperature, ethene can react with oxygen to form products.

Analyze the given options

Let's analyze each option and see if it can be formed as a product from the reaction of ethene and air: (a) Epoxy ethane: This is formed by the addition of oxygen to ethene. (b) Ethanal: This is formed by the partial oxidation of ethene. (c) Ethanoic acid: This is formed by the complete oxidation of ethene. (d) Methanal: This cannot be formed as a product from the ethene reaction since it contains only one carbon atom, while ethene has two carbon atoms.

Choose the correct product

Considering the reaction conditions (silver catalyst and 500 K temperature), the most probable product to form is the one from the partial oxidation of ethene. This option is (b) Ethanal. So, the product formed when ethene and air under pressure is passed over a silver catalyst heated to 500 K is Ethanal (b).

Key concepts

Ethene Reactions

Ethene is an important organic compound, also known as ethylene, with the formula \(C_2H_4\). It is the simplest alkene, a class of hydrocarbons that have at least one carbon-carbon double bond. The presence of this double bond makes ethene highly reactive and able to undergo various chemical reactions.

Some key reactions of ethene include:

• Addition Reactions: Ethene readily participates in addition reactions due to the double bond, which can open up to add other atoms or groups. This includes reactions with halogens, hydrogenation to form alkanes, and hydration to produce alcohols.
• Oxidation Reactions: Ethene can be oxidized under different conditions to form a variety of products. With mild oxidation, it can produce compounds like ethanal (acetaldehyde); with stronger oxidation agents, it can lead to the formation of ethanoic acid (acetic acid).
• Polymerization: Ethene is a key monomer in the production of polyethylene, a widely used plastic.

Understanding these reactions is crucial for many industrial chemical processes and helps illustrate the versatility of ethene in organic chemistry.

Oxidation Reactions

In chemistry, oxidation reactions involve the transfer of electrons, leading to a change in the oxidation state of molecules. Specifically, it often involves the addition of oxygen to a compound or the removal of hydrogen.

For ethene, oxidation can occur in different ways depending on the conditions and the presence of catalysts. Key oxidation reactions of ethene include:

• Partial Oxidation: When ethene is partially oxidized, typically in the presence of a catalyst like silver at elevated temperatures (e.g., 500 K), it forms ethanal (acetaldehyde). This type of reaction requires precise control over reaction conditions to avoid further oxidation.
• Complete Oxidation: If oxidation proceeds completely, ethene can be converted into ethanoic acid. This reaction involves further addition of oxygen and usually stronger oxidizing agents or conditions.

Recognizing the type of oxidation reaction and the factors influencing it is vital for controlling the desired product formation in industrial and laboratory settings.

Catalysis in Chemistry

Catalysis is a process where the rate of a chemical reaction is increased by adding a substance known as a catalyst. The catalyst itself is not consumed in the chemical reaction, meaning it can be recovered unchanged at the end of the reaction.

In the reaction of ethene with air, silver acts as a catalyst for the partial oxidation of ethene to ethanal, especially at high temperatures like 500 K. Utilizing catalysts in chemical reactions is fundamental due to the following reasons:

• Lowering Energy Enhancements: Catalysts can lower the activation energy required for a reaction to occur, making the process more efficient and faster.
• Direction and Selectivity: Catalysts not only speed up reactions but can also guide them to produce specific products over others. This selectivity is key in reactions involving multiple possible pathways, as seen in the oxidation of ethene to ethanal.
• Economical Advantages: Catalysts allow reactions to occur under less harsh conditions (e.g., lower temperatures or pressures), potentially reducing energy costs and material expenses.

Catalysis is a cornerstone of industrial chemistry, providing unexpected pathways and more sustainable options for producing chemicals.