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Ch.14 - Chemical Kinetics
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All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 81b

Chapter 14, Problem 81b

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 1Al2O32 or silica 1SiO22. (b) How does the surface area affect the rate of reaction?

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Hey everyone. So today we're being told that marble is a crystalline form of calcium carbonate and can react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. And we're being asked how the surface area of the reactant which in this case is marble affects the rate of the reaction and comparing it from marble chunks and marble powder. So this reaction, let's write it out. We have calcium carbonate, C zero cc O C A C A C 03, which is a solid, Reacts with two moles of hydrochloric acid, which is a curious to form calcium chloride, CACL two, C 02 and water. So since we're in a or since a cl is an aqueous solution and marvel is a solid, we can say that the the reaction between marvel and hydrochloric acid is heterogeneous. And one thing we know about heterogeneous reactions Janice is that they are affected by the surface area of one or more of the reactant. So if we consider solid marble, let's try this out and rent. If we consider just a solid slab of marble, it's very smooth, it's very big. But the total surface area would actually be far less compared to a powdered version. And I'll just draw this as a little a little mound of powder and this is because on the powder, every single surface in the powder can react to the hcl while in the in the chunk or in the slab of marble. Everything that is inside is protected by the outside. So the hydrochloric acid will have a much harder time of getting into and reacting with as much of the marble than it would if the marble was mixed into the hydrochloric acid as a powder, therefore having more surface area having more surface area, which is the powdered form this area powder will increase the rate of the reaction, increases reaction rate. I hope this helps, and I look forward to seeing you all in the next one.
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