Video Transcript
A chemist performs a series of
experiments to determine the effect of concentration on the rate of a reaction. They pour an equal amount of
hydrochloric acid of different concentrations into four test tubes. Then they place an identical piece
of magnesium ribbon into each of the test tubes. The experiment setup is shown
below. From slowest to quickest, what is
the likely ordering of the rate of reaction for the four experiments? (A) A, C, D, B. (B) B, C, A, D. (C) C, D, B, A. (D) D, C, A, B. Or (E) C, A, B, D.
In each of the test tubes, an
identical piece of magnesium ribbon is submerged in the same volume of hydrochloric
acid. The test tubes differ in the
concentration of hydrochloric acid used, given here in moles per liter. Concentration is a measure of the
amount of substance in a given volume. We need to determine how the
different concentrations of hydrochloric acid in each test tube will affect the rate
of reaction. Let’s clear some space at the top
of the screen.
The rate of a reaction measures how
reactant or product concentration, mass, or volume changes per unit of time. We can think of this as the speed
of a chemical reaction. In order for a chemical reaction
between two particles to occur, the particles must collide with one another with a
certain amount of energy. This means that some collisions
won’t result in a reaction. But if we can increase the total
number of collisions, we can increase the chance that a reaction will occur, thus
increasing the rate of reaction.
So how does changing the
concentration affect rate of reaction? Let’s consider the sample of pink
and orange particles. These particles will have a certain
number of collisions with one another. Increasing the concentration of
pink particles means that there will be more pink particles available to collide
with the orange particles. The number of collisions will
increase, and the rate of reaction will increase. So increasing the concentration
increases the rate of reaction.
We want to order the experiments
from slowest to quickest. If increasing the concentration
increases the rate of reaction, then we should put the experiments in order from
lowest concentration to highest concentration. At 0.1 moles per liter, (B) has the
lowest concentration, followed by (C), then (A), then (D), with the highest
concentration at 5.0 moles per liter. So the correct answer for the
likely ordering of the rate of reaction for the four experiments from slowest to
quickest is answer choice (B) B, C, A, D.
