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.
