Video Transcript
Which of the following is not a
common unit used when measuring the rate of a chemical reaction? (A) Liters per minute, (B) grams
per second, (C) moles per minute, (D) meters per second, or (E) cubic centimeters
per second.
Chemical reactions take place at
different speeds. Some reactions, such as explosions,
happen very quickly. Other reactions, such as rusting,
happen over a long period of time. As a reaction takes place,
reactants form products. The concentration of the reactants
decreases, and the concentration of the products increases. This describes the rate of a
reaction, which is defined as the change in concentration of a reactant or product
per unit of time.
The question is asking us, “Which
of the given units is not commonly used when measuring the rate of a reaction?” To measure the rate of a reaction,
we need a unit that can be used to measure the quantity of a substance per unit of
time. Looking at the five answer choices,
all of our options are either per minute or per second, which are all suitable units
with which to measure time. We will have to look at the first
part of these units to identify which unit would not be suitable for measuring the
amount of a substance and thus the correct answer.
Let’s start with answer choice (A)
liters per minute. Liters can measure a volume of
substance produced or consumed in a reaction. Since this unit would measure a
change in volume of substance per minute, it is a suitable unit to measure the rate
of a reaction. And so it is not the answer to this
question.
Answer choice (B), grams per
second, and (C), moles per minute, feature units which measure amount of matter. Changes to amounts of matter
measured in grams per second or moles per minute are conceivable units to measure
rates. So these answer choices can be
eliminated.
Answer choice (E), cubic
centimeters per second, measures a change in volume per second, which could be
measured with an apparatus, such as a gas syringe. Since this unit would measure a
change in volume of a substance per unit of time and could thus be used to measure
the rate of a reaction, it can be eliminated.
This leaves us with answer choice
(D) meters per second. A meter is a unit of measurement
for a length. So meters per second would measure
the change in a distance over time. This unit would not be commonly
used to measure changes in reactants or products in a chemical reaction and so would
not be a useful unit to measure reaction rates. Answer choice (D) is the correct
answer.
Therefore, the unit that is not a
common unit used when measuring a rate of a chemical reaction is answer choice (D)
meters per second.
