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).
