Video Transcript
Which of the following lines
depicts the points at which dynamic equilibrium is established?
Dynamic equilibrium is an
equilibrium between forward and reverse reactions where both reactions occur at the
same nonzero rate. To answer the question, we need to
determine which of the lines depicts the points at which dynamic equilibrium has
been established. To do this, let’s take a closer
look at the graph. The 𝑦-axis represents the
percentage of reactants and products. We can see that the blue line is
initially at 100 percent, so this line must represent the reactants. The green line is initially at zero
percent, so this line must represent the products.
As dynamic equilibrium is
established when both the forward and reverse reactions have the same rate, let’s
consider how the rate of the forward and reverse reactions will change over
time. Initially, there is some amount of
reactants and zero products. As time passes, some of the
reactants will be converted into products. So, the percentage of reactants
will decrease and the percentage of products will increase. As the products begin to be made,
the rate of the forward reaction begins to slow as there are fewer reactant
molecules available to react. Simultaneously, as the reaction is
reversible and there are now more product molecules available to react, some of the
products will be converted into reactants and the rate of the reverse reaction will
begin to increase.
As more time passes, the percentage
of reactants will continue to decrease and the percentage of products will continue
to increase. At the same time, the rate of the
forwards reaction will continue to slow and the rate of the reverse reaction will
continue to speed up. Eventually, a point is reached
where the forward and reverse reactions occur at the same rate. This is the point at which dynamic
equilibrium is established. At this point, as reactants are
being converted into products, the products are being converted back into reactants
at the same rate. Even though both reactions are
still occurring, because the rates are the same, there is no net change in the
amount of the reactants or products.
So, when looking at the provided
graph, we can determine when dynamic equilibrium is established by identifying the
point at which the percentages no longer change. We can see that the percentages
begin to remain constant starting from line C. The percentages are still constant
at line D. This indicates that dynamic
equilibrium is still occurring. So, while both lines C and D
represent points at which the reactions are in dynamic equilibrium, we want to know
which line represents when dynamic equilibrium is established. Dynamic equilibrium is established
when the percentages first begin to remain constant. This occurs at line C.
Therefore, the line that depicts
the points at which dynamic equilibrium is established is C.
