Which of the following is not a
viable unit for a reaction rate? (A) kg over s, (B) g over s, (C) h
over s, (D) M over min, or (E) t over d.
Let’s start by working out what all
of these symbols stand for. (A) stands for kilograms per
second. (B) is similar, grams per
second. (C) is hours per second. (D) is molars per minute,
remembering that molar means moles per liter, sometimes written as moles per
decimeter cubed. And (E) is tons per day. To work out what a sensible unit
for reaction rate is, let’s remind ourselves what we mean by rate of reaction.
The rate of a reaction is the rate
that to the reactants are turning into the products. To measure the rate of reaction, we
could measure the loss of our reactants or we could measure the formation of our
products. Either way, we’re using a similar
equation. We can calculate the rate of
reaction by doing the mass or amount of our product formed or the mass or amount of
our reactant lost divided by time.
So the units for our mass or amount
will be things like kilograms, grams, moles, et cetera. And the units of time will be
seconds, minutes, hours, et cetera. So we’re looking for units along
the lines of kilograms per second, grams per minute, moles per hour, et cetera. We can see that (A), (B), (D), and
(E) all follow this pattern, while (C) does not. So this is our correct answer.