Video Transcript
Which of the following statements
concerning the effect of concentration on the rate of reaction is correct? (A) Increasing the concentration
increases the number of particles present; there is a greater number of collisions,
and so the rate of reaction decreases. (B) Increasing the concentration
increases the number of particles present; there is a greater number of collisions,
and so the rate of reaction increases. (C) Increasing the concentration
increases the number of particles present; there are fewer collisions, and so the
rate of reaction decreases. (D) Increasing the concentration
decreases the number of particles present; there is a greater number of collisions,
and so the rate of reaction increases. (E) Increasing the concentration
decreases the number of particles present; there are fewer collisions, and so the
rate of reaction decreases.
Concentration is the amount of
substance in a particular volume. Increasing the concentration means
that there is more substance in the same volume, while decreasing the concentration
means that there is less substance in the same volume.
If we look at the answer choices,
we can see that answer choices (D) and (E) incorrectly describe increasing
concentration as a decrease in the number of particles present. Let’s remove these incorrect answer
choices so we can discuss how concentration affects the rate of reaction.
Rate of reaction measures how
reactant or product concentration, mass, or volume changes over time. We can think of the rate of
reaction as the speed of a chemical reaction. The rate of reaction is closely
related to the number of collisions that occur between reactant particles per unit
of time. In order for a reaction to take
place, particles must successfully collide with the correct orientation and
sufficient energy. If the number of collisions between
reactant particles increases, then the chance of a successful collision will
increase and the rate of reaction will increase.
To help us understand how
concentration affects the rate of reaction, let’s consider two experiments involving
the reaction between a metal and an acid. In one experiment, a low
concentration of acid is used. And in the other experiment, a high
concentration of acid is used. We know that the experiment using a
high concentration of acid will have more acid particles per unit of volume than the
experiment with a low concentration. The more particles present, the
greater the number of collisions between the acid particles and the metal. And we know that as the number of
collisions per second increases, the rate of reaction increases. So the reaction using a higher
concentration of acid will be faster.
From our discussion, we now know
that the statement concerning the effect of concentration on the rate of reaction
that is correct is answer choice (B). Increasing the concentration
increases the number of particles present; there is a greater number of collisions,
and so the rate of reaction increases.
