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Question Video: Understanding How Catalysts Work Chemistry • 7th Grade

Which of the following statements explains how catalysts increase the rate of reaction? [A] Catalysts are consumed in the reaction, providing a greater surface area. [B] Catalysts provide an alternate chemical pathway with a lower activation energy. [C] Catalysts provide alternate conditions with the same chemical pathway. [D] Catalysts are consumed in the reaction, providing an alternate chemical pathway. [E] Catalyst provide an alternate pathway with higher activation energy.

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Video Transcript

Which of the following statements explains how catalysts increase the rate of reaction? (A) Catalysts are consumed in the reaction, providing a greater surface area. (B) Catalysts provide an alternate chemical pathway with a lower activation energy. (C) Catalysts provide alternate conditions with the same chemical pathway. (D) Catalysts are consumed in the reaction, providing an alternate chemical pathway. (E) Catalyst provide an alternate pathway with higher activation energy.

A catalyst is a substance that increases the rate of a chemical reaction. But a catalyst is never chemically changed by the end of the reaction. So right away, we can eliminate answer choices (A) and (D). Since catalysts are not chemically changed by the end of the reaction, they are never consumed in the reaction.

But let’s return to the question. How do catalysts increase the rate of reaction? To answer this, we’ll refer to this reaction diagram. This amount of energy right here is called the activation energy. The activation energy is the minimum amount of energy that’s needed for a reaction to occur. If particles don’t have this amount of energy when they collide with each other, no reaction will happen. Catalysts increase the rate of reaction because they provide an alternate way for the reaction to progress that has a lower activation energy. Answer choice (B), catalysts provide an alternate chemical pathway with a lower activation energy, seems to match this best.

An example of catalysts at work in industry is the Haber–Bosch process. The Haber–Bosch process is the industrial synthesis of ammonia from nitrogen and hydrogen gas for use in fertilizers. The reaction between nitrogen and hydrogen has a very high activation energy. So the reaction doesn’t happen under normal conditions. So an iron catalyst is used. Nitrogen and hydrogen particles can adsorb onto the iron catalyst’s surface. Then, the molecules dissociate, or break apart, into atoms of nitrogen and hydrogen. Individual atoms of hydrogen then bond to the nitrogen atoms one by one. The ammonia molecules that are formed are then released, or desorbed, from the surface of the catalyst.

The reaction using the catalyst requires far less energy than the reaction between nitrogen and hydrogen atoms on their own, which is why all catalysts increase the rate of reaction. Catalysts provide an alternate chemical pathway with a lower activation energy. This matches answer choice (B).

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