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 \(\left(\mathrm{Si} \mathrm{O}_{2}\right)\) (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?

Catalysis is a process in which a substance called a catalyst speeds up a chemical reaction without being consumed in the reaction. Catalysts work by lowering the activation energy required for a reaction to occur, allowing the reaction to happen faster and more efficiently.

Surface area plays a critical role in the rate of reaction, especially in heterogeneous catalysis, where the catalyst is in a different phase than the reactants. The larger the surface area, the more reactant molecules can come in contact with the catalyst, allowing for more simultaneous reaction sites and, hence, a faster overall reaction rate.

Depositing metallic catalysts as thin films on high surface area substances such as alumina or silica is more effective than using powdered metals for several reasons: 1. Higher surface area: By depositing the catalyst as a thin film, the catalyst's overall surface area is increased, which allows more reactant molecules to come in contact with the catalyst, leading to a faster reaction rate. 2. Improved catalyst utilization: A thin film of catalyst allows reactants to access the catalyst more easily compared to powdered metals, ensuring the catalyst material is being used more efficiently. 3. Enhanced stability: Thin films are less likely to become contaminated or degraded, ensuring a more consistent performance and better longevity of the catalyst.

As discussed earlier, the surface area of the catalyst directly affects the reaction rate in heterogeneous catalysis. A larger surface area means that there are more available sites on the catalyst where reactant molecules can interact. This effectively increases the chances of fruitful collisions between reactant molecules and catalyst, thus enhancing the reaction rate. In essence, the larger the surface area of the catalyst, the more efficient and faster the reaction will be. In conclusion: a) Depositing metallic catalysts as thin films on high surface area substances is more effective than using powdered metals because it provides a higher surface area for reactants to interact and ensures more efficient catalyst utilization with better stability. b) The surface area directly affects the rate of reaction by providing more available sites for reactant molecules to interact with the catalyst, increasing the chances of fruitful collisions and a faster reaction rate.