This week was another continuation of equilibrium. However,
this time we combined a little bit of thermodynamics and what they can tell us
about a reaction at equilibrium. We were also introduced to Q, which serves as
an indicator of the state of a reaction and what needs to occur in order for
that reaction to proceed towards equilibrium.
I’ll admit that equilibrium is not a very solid topic for
me, but I can feel myself gain more clarity on the subject each day in class. A
few misconceptions about equilibrium were cleared up for me this week.
Previously, it was difficult for me to grasp the difference between
concentration and rates. I had thought that equilibrium meant that there was an
equal amount of products and reactants. However, this is not the case. There
could be much more reactants than products at equilibrium or vice versa, and
therefore the concentrations could be much different. Equilibrium is when these
concentrations stay constant, and the rates of the forward and reverse
reactions are the same.
This week was very heavy with emphasis on Le Chatelier’s
principle, which states that when stress is placed on a reaction, the reaction
proceeds in the direction that counteracts that stress. We continued using
ConcepTests that had us think about questions involving Le Chatelier’s
principle, and went through various reaction scenarios. Some involved adding a
reactant or product, and others involved decreasing or increasing the volume or
temperature. As usual, these ConcepTests were very useful for me and helped me
understand a few key points regarding equilibrium. They’re actually fun, too,
especially when we hear about other classes having heated debates over one
question.
We were introduced to RICE tables which serve as an
organizing strategy to observe the change in a reaction as it proceeds towards
equilibrium.
Dr. J really started to crack down on us this week. In order
to further help us understand equilibrium, he had to resort to desperate
measures—now we have to turn in our completed lecture worksheets for point! And
perhaps even worse, we have started MetaLogs, which serves as a class
note-taking strategy for lectures during class. However, although I hate to say
it, MetaLogs are quite helpful for me. During our first equilibrium simulation,
I felt several “oh, I get it!” moments as I wrote something down on my logs.
Putting these thoughts on paper not only gave me examples I could refer back
to, it also helped me make some connections that were obscure to me before.
On Friday, we did another simulation involving NO2, a brown
gas, and colorless N2O2. We reviewed what it meant when a reaction was endo or
exothermic, and then tried to figure out which one the reaction we had was.
Having taken in the brown-hued gas into two different syringes, we performed
some mini experiments on them. In order to figure out what type of reaction it
was, we immersed both syringes into water—one in hot water and one in cold—and
observed any changes. The syringe in the hot water became a more concentrated
brown, while the syringe in cold water became lighter. Because NO2, the
reactant, is a brown gas, this meant that the syringe in hot water contained
more reactants. Thus, stress was placed on the products side. The reaction
proceeded towards the reactants side to lessen this stress. The “stress” we
placed on the system was increasing the temperature, so heat would be placed on
the products side. Therefore, this was an exothermic reaction.
We also compressed and expanded the syringes to observe any
changes in color. For example, when we compressed the syringe, the gas turned
dark immediately, and gradually because lighter once again.
Although equilibrium is a broad and sometimes obscure topic,
I can feel myself become more confident with it as we go on and discuss the
workings behind it, along with running simulations and working through
problems.
