Many metallic catalysts, particularly the precious-metal ones, are often deposited as very thin films on a substance of high surface area per unit mass, such as alumina \(\left(\mathrm{Al}_{2} \mathrm{O}_{3}\right)\) or silica \(\left(\mathrm{SiO}_{2}\right)\). (a) Why is this an effective way of utilizing the catalyst material compared to having powdered metals? (b) How does the surface area affect the rate of reaction?

Depositing metallic catalysts (especially precious metals) on high surface area substances like alumina (Al2O3) or silica (SiO2) is more effective compared to using powdered metals because of the following reasons: 1. Surface area utilization: A higher surface area of the catalyst means that more reaction sites are available for the reacting molecules, leading to faster reaction rates. Thin films of the catalyst on these high surface area substances increase the number of catalyst sites, thus making the process more efficient. 2. Reduction of costs: Precious-metal catalysts are often expensive, so utilizing them in the form of thin films can significantly reduce the amount of catalyst material needed for the process. This reduces the overall cost of the process and makes it more economically feasible. 3. Enhanced stability: Depositing catalysts on supports like alumina or silica also helps in stabilizing the catalyst particles, preventing them from interacting with each other and forming larger particles, which would reduce the surface area available for the reaction.

The surface area of a catalyst directly impacts the rate of reaction due to the following reasons: 1. Higher surface area leads to more reaction sites: When the surface area of a catalyst is increased, there are more reaction sites available for the molecules of the reactants to interact with the catalyst. This leads to faster reaction rates. 2. Increased probability of collisions: A catalyst with a larger surface area offers more chances for reactant molecules to interact with its surface, thus increasing the probability of a successful collision and thereby enhancing the reaction rate. 3. Facilitates better adsorption and desorption of reactants: A higher surface area enables more reactants to be adsorbed onto the catalyst's surface, which can facilitate the activation of bonds and the formation of activated complexes. Likewise, a higher surface area also allows for better desorption of the products, making room for more reactant molecules to interact with the catalyst. In conclusion, an increased catalyst surface area can significantly enhance the rate of reaction by providing more reaction sites, increasing the probability of successful collisions, and facilitating better adsorption and desorption of reactants and products.