Blog Entry 2/9/14

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.

Blog Entry 1/19/14

This week in AP chemistry was filled with much more exciting experiments than usual. In class, we performed the experiments many people expect out of a chemistry class: freezing random things, harmlessly setting students’ hands on fire, and freaking out random passerby by pouring suspicious substances near them. On Thursday and Friday, we performed many demos with said suspicious substance: liquid nitrogen! I have to say this was probably one of my favorite weeks in chemistry; learning about a reaction is one thing, but seeing it in action is just plain cool.

We started off the week by completing a few more lecture quizzes on Kinetic Molecular Theory and partial pressures. Recently, we have been starting to participate in ConcepTests as a class much more frequently. Of all the ways we use to go over material in class, I think I’ve found ConcepTests most helpful. Although I find whiteboarding helpful, I sometimes don't have time to finish all of the problems before we go over them, which makes me become confused and a little overwhelmed when we move through each group’s board and their process quickly.

ConcepTests allow for a little more independent thinking. We are given a question on the projector, and asked to think about it and hold up the fingers that correspond to the answer we choose. It’s kind of like a voting system, and it’s very interesting when the class comes up with a broad spectrum of different answers. After voting individually, we discuss the question as a group and agree on one answer. I really like this system because I have to process and solve the question on my own before talking with my group mates. I am able to reach an answer myself without coasting on someone else’s answer and just agreeing with it.

After discussing the question, we go over the question as a class and Dr. J makes sure all of us understand the process used to reach an answer. I don’t ever feel left behind when we use this method, and I feel much more involved in the class.  

The most exciting part of the week was undoubtedly the liquid nitrogen demo. There were many collective “ooohs” and “aaaahs” as we froze objects to our hearts’ desire. We started off with a bouquet of flowers, and went to freezing grapes. We however were not satisfied there, oh no! We continued freezing miscellaneous objects from squash balls to marshmallows. We even froze money! Talk about some pretty cold currency.  I had a frozen marshmallow herself due to my extremely good luck being picked in the Chemistry Volunteer Lottery. Most of my classmates lingered afterwards to try a marshmallow of their own, so of course everyone went home happy.

This demo was not just fun and games, however. We discussed much of the science behind the substances and the behavior of the molecules involved. In one demo, we boiled water by using ice, and little droplets of liquid oxygen condensed on the desk.

The day after we played with something leaning more on the hot side: fire. We bubbled methane over water and some students picked up a handful of large methane bubbles, which were then promptly set on fire by Dr. J. The smell of charred hair might have filled room B403, but it’s not everyday when you get to set your hands on fire and emerge unscathed.

This week in chemistry was a lot of fun, while still being able to be a learning experience. I’m hoping to perform more demos in the future in class!