May 20-24

This week, I learned about endothermic and exothermic reactions. Not only did I learn this, but I also revisited some content from Unit 6 pertaining to the energy bar graphs and even came up with the concept of the transfer of chemical energy through these reactions.

This shows that in the exothermic reaction, the reactants require
more energy to bond than do the reactants in the endothermic
reaction. In the endothermic reaction, the products require more
energy to bond than do the reactants.

But, first, let's first revisit the iron and copper (II) chloride lab. One of the observations I made during the lab was that as the iron nail reacted with the CuCl2, the temperature increased. I knew the temperature was increasing because when I felt the beaker, it felt warmer than previously. Therefore, a chemical reaction occurred in the beaker. Not only this, but energy was also transferred from the aqueous solution to the surface of the glass beaker.

As energy transferred out of the system, the atoms were rearranged. This makes sense because energy was required to break apart the copper and the chlorine. Hence, copper and chlorine were dissociated and formed into neutrally charged ions.

Initially, copper had a charge of +2 while Cl2 had a charge of -1 per chlorine atom. When they were separated, though, the energy transferred to them, dissociating them and transferring electrons. Since the copper has a positive charge (as all metals do), it needed to gain 2 e- (electrons are negatively charged) to neutralize its charge. Hence, the diatomic chlorine lost 2 e-, making it more positive and neutrally charged.

On top, copper is collected on left tube.
On bottom, copper is collected on right tube.

In order to bond the two together, though, they are both put into water in an electrolysis kit to form an aqueous solution. As I've mentioned before, the copper and the chloride separated from each other due to energy. But, where did the energy come from? Obviously, whatever was hooked up to the electrolysis kit! In this case, it was the genecon. The electrons from chloride to copper were transferred from the chloride (right) to the copper (left). In one of the previous, I questioned what would happen if the genecon were turned counter clockwise? It turns out that it doesn't really matter because the electrons are still transferred from the chloride to the copper–just in a counter clockwise direction. Either way, the genecon enabled the electrical current it produced to carry the electrons from one substance to another to neutralize the charges and to separate.

As a result, we came to the conclusion that chemical energy inherently was a major part in this experiment. From this, we learned how to use the LOL diagram charts to graph it. But, the question is how and what would the changes in the ph and th accounts be?

We know that from the experiment with the iron nail and the copper chloride that the iron chloride formed and that the copper precipitate formed. When they reacted, energy escaped the system. But how? When they chemically reacted, a chemical reaction occurred, but of course was used up as soon as all the moles of iron and copper chloride that could possibly react together (of course, the amount is limited depending on the ratios). Hence, after the reaction occurred, chemical energy escaped from the system. The same way worked with thermal energy. As the reaction occurred, the beaker got warmer. Hence, the chemical energy that escaped the system was converted into thermal energy, which of course also was released from the system since the beaker gradually cooled down afterwards.

As I said up top, I would discuss endothermic and exothermic reactions. What occurred here was clearly an exothermic reaction because energy was released from this system. In the reaction, it took more energy to bond together the copper chloride than the iron chloride. Of course, one could say that it took more energy to bond iron and chloride or else they wouldn't be bonded. These both sound plausible, but what is actually happening? Let's considered that in the experiment, there was an excess amount of iron left, which meant that enough energy was used to separate the copper and the chloride and bond the iron to the chloride. Of course, it took more energy to separate the copper and the chloride because it requires more energy to bond than iron chloride. This makes sense because copper has a huger molar mass (63.54 g/mol) than iron (55.85 g/mol). Logically, it would take more energy to take apart something with a greater mass just as much as it would take a greater force (twice as much) to move an object of 200 lbs from x distance and half as much required for the larger object to push the 100 lb object. I noticed a trend that the greater the molar mass, the greater the number of electrons. This would explain why more energy was used to bond copper chloride than iron chloride.

This would also make sense because once the electricity passes through iron, it becomes magnetic, and since less energy is required to bond iron to chloride, this would mean that some of the energy is being used to make it magnetic. However, since some chemical energy has been used up to form a new substance and rearrange the particles, it becomes less magnetic than iron itself.

Therefore, the reactants in an exothermic reaction have greater chemical energy than the energy in the products because some of that energy has already been used up.

This week, however, we have not really looked into endothermic reactions, but endothermic reactions are the opposite. Instead of leaving the system, energy enters the system. This would mean that there was less chemical and thermal energy to begin with, but when the reaction occurred, energy was needed in the system, so the products made required more energy than the reactants. When the alka seltzer is put in the water, for example, a gas is created. But, was it created from the energy that entered the system? This is where it gets confusing. Hopefully, this is something I can put energy into studying next week and for AP Chem next year.