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Question Video: Identifying the Statement that Does Not Accurately Describe a Benefit of a Catalyst Chemistry • 7th Grade

Which of the following is not a benefit of using catalysts in industrial processes? [A] The products are made more quickly. [B] Reactions can operate at lower temperatures. [C] Catalysts do not need to be replaced often. [D] Reactions can operate at lower pressures. [E] Catalysts are often rare transition metals.

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Video Transcript

Which of the following is not a benefit of using catalysts in industrial processes? (A) The products are made more quickly. (B) Reactions can operate at lower temperatures. (C) Catalysts do not need to be replaced often. (D) Reactions can operate at lower pressures. Or (E) catalysts are often rare transition metals.

Catalysts are substances that increase the rate of reaction without undergoing a permanent chemical change. Catalysts increase the rate of reaction by providing an alternate reaction pathway that has a lower activation energy. Let’s consider the reaction between nitrogen and hydrogen to produce ammonia.

This reaction has a high activation energy, so a lot of energy needs to be supplied in order for the reaction to occur. The activation energy could be overcome by heating up the reaction system greatly or by significantly increasing the pressure. As a lot of energy is required, this reaction will proceed rather slowly.

Adding a catalyst, like iron, lowers the activation energy. This means the reaction can operate at lower temperatures and lower pressures. As less energy is required for the reaction to proceed, the product will be made more quickly. The iron catalyst lowers the activation energy and increases the rate of reaction by providing an alternate reaction pathway. Let’s examine this alternate reaction pathway.

First, the reactant molecules absorb onto the iron catalyst surface and dissociate into atoms of nitrogen and atoms of hydrogen. Then, three hydrogen atoms react with and bond to a nitrogen atom one at a time. Finally, the ammonia is released or desorbed from the catalyst surface. We can see that although the iron catalyst is involved in the reaction, at the end of the reaction it is chemically unchanged. So, a very small amount of catalyst can be used again and again to catalyze a large amount of reactants.

From our discussion, we’ve seen that using a catalyst allows for products to be made more quickly and reactions can operate at lower temperatures and pressures. We’ve also seen that catalysts do not need to be replaced often as they don’t undergo a permanent chemical change during the reaction. These are all benefits of using catalysts in industrial processes.

However, we want to know which of the answer choices is not a benefit of using catalysts. So, we can eliminate answer choices (A) through (D). This leaves us with the answer choice (E): catalysts are often rare transition metals. While our example reaction used an iron catalyst, it’s not uncommon for catalysts to be composed of rare transition metals, like rhodium, palladium, or platinum. As these transition metals are rare, they are very expensive.

Therefore, the answer choice that is not a benefit of using catalysts in industrial processes is answer choice (E). Catalysts are often rare transition metals.

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