Question

In the preparation of alkene from alcohol using \(\mathrm{Al}_{2} \mathrm{O}_{3}\), which is the most effective factor? (a) Porosity of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (b) Temperature (c) Surface area of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (d) Concentration

Short answer

Surface area of \( \mathrm{Al}_{2} \mathrm{O}_{3} \) is the most effective factor.

Step-by-step solution

Understand the Context of the Reaction

In this exercise, we're looking at the dehydration of alcohols to form alkenes. This process is often catalyzed using solid catalysts like \( \mathrm{Al}_{2} \mathrm{O}_{3} \). The reaction generally relies on a catalyst and certain reaction conditions to proceed effectively.

Identify the Role of Catalyst Properties

The effectiveness of a catalyst in a reaction like this can depend on various physical properties such as porosity, surface area, and the conditions like temperature. These factors can influence the rate at which the reaction occurs and the yield of the desired product, which in this case is an alkene.

Analyze the Options Given

Consider each of the factors listed: (a) Porosity of \( \mathrm{Al}_{2} \mathrm{O}_{3} \) affects how easily reactants can diffuse and make contact with reactive sites.(b) Temperature influences reaction kinetics, enabling or accelerating the reaction.(c) Surface area of \( \mathrm{Al}_{2} \mathrm{O}_{3} \) is crucial because more area means more active sites for the reaction.(d) Concentration primarily affects solution reactions and may be less significant here.

Evaluate the Most Effective Factor

For solid catalysts like \( \mathrm{Al}_{2} \mathrm{O}_{3} \), the surface area is often the most immediately impactful factor. The larger the surface area, the more active sites are available for the reaction to occur, leading to increased reaction rates and yield efficiency.

Conclude the Solution

Based on the analysis of the role of each factor, the surface area of the catalyst is key to maximizing the effect of \( \mathrm{Al}_{2} \mathrm{O}_{3} \) in the dehydration of alcohols. Hence, surface area is usually the most effective factor.

Key concepts

Dehydration of Alcohols

Dehydration of alcohols is a chemical reaction where water is removed from an alcohol molecule to form an alkene. This process is key in organic chemistry for synthesizing alkenes, which are essential building blocks in many industries, including petrochemicals and pharmaceuticals.
This transformation is typically carried out using a catalyst, often an acid, to facilitate the removal of the hydroxyl group and a hydrogen atom from the alcohol. Given that alkenes are more stable than the alcohols from which they are prepared, this reaction is quite favorable.
The typical reaction is written as: \[ ext{C}_n ext{H}_{2n+1} ext{OH} ightarrow ext{C}_n ext{H}_{2n} + ext{H}_2 ext{O} \]
This shows the breakdown of an alcohol (like ethanol) into an alkene (such as ethene) and water. Solid catalysts, such as \( ext{Al}_2 ext{O}_3 \), are often utilized to provide the necessary surface for reaction.

Solid Catalysts

Solid catalysts are substances that increase the rate of a reaction without being consumed in the process. They provide a surface on which the reactants can come together more easily.
Think of a solid catalyst as a matchmaker for molecules. In the dehydration of alcohols, \( ext{Al}_2 ext{O}_3 \) is a commonly used solid catalyst. It facilitates the removal of water from alcohol and promotes the formation of a double bond, leading to the creation of an alkene.
Solid catalysts are reusable and can be more efficient than liquid catalysts. Unlike liquid catalysts, they can be easily separated from the reaction mixture and reused, making them more sustainable choices in industrial applications.

Catalyst Surface Area

The surface area of a solid catalyst is a critical factor affecting its effectiveness. The larger the surface area, the more "active sites" are available for the reaction to take place.
Active sites are areas on the surface where the reaction occurs. More surface area means more molecules can be in contact with the catalyst simultaneously, leading to faster conversion rates.
This is why in reactions like the dehydration of alcohols using \( ext{Al}_2 ext{O}_3 \), increasing the surface area of the catalyst can lead to a greater yield of alkenes. Techniques such as increasing porosity or particle size can be used to maximize the surface area of the catalyst.

Reaction Kinetics

Reaction kinetics involves the study of the speed at which chemical reactions occur and the factors that influence these rates. Catalysts, temperature, and concentration are all critical in this context.
For dehydration reactions, catalysts are key players because they lower the energy barrier, allowing the reaction to proceed at a faster rate and often at lower temperatures. Temperature itself is another major factor in reaction kinetics; higher temperatures generally increase molecular movement, thus increasing the frequency of collisions between reactant molecules.
In the context of solid catalysts such as \( ext{Al}_2 ext{O}_3 \), both temperature and surface area collaborate to optimize reaction speeds and efficiency.