Last week we had a major focus on entropy of reactions and how entropy of reactions work. This week was probably the most difficult to understand so far. Entropy is a difficult concept for me to understand, especially with all the equations needed to calculate values. The basic definition of entropy is the number of distinguishable micro states in a given system. Evaluating if entropy increases or decreases in a reaction is relatively easy, if the number of particles or the energy of the particles increase, then the entropy increases. Entropy always increases in the universe.

In addition to entropy, we also worked on several other thermodynamic principles, one being Gibbs free energy. This free energy, as it is called, is energy in a reaction that can be used to do work on the system or for the system to do work on the surroundings. The equation for Gibbs free energy is ∆G=∆H-T∆S, where ∆H is enthalpy, T is time, and ∆S is entropy. Enthalpies and entropies are usually given in a table, but can be calculated using this equation if the free energy was known I suppose. This ∆G, or free energy, can be used to determine if a reaction is thermodynamically favored or not. If ∆G is negative, then the reaction is favored and will "go" without any outside energy needed. For example, dry ice sublimes at room temperature because it is favored. But water does not boil at room temperature because the ∆G of that reaction is positive.

Another thermodynamic principle is Hess' law. Hess' law states that in a reaction, the sum of the enthalpy of the steps of a reaction can be added up to to equal the total enthalpy of the reaction. My understanding of this is that if you add up the bond enthalpies in each different step and them cancel out the ones that are on both sides and eventually you will come to the total heat of reaction or the enthalpy of the reaction. Here's a link to a site on Hess' law.

Overall, my understanding of this unit so far is not where I would like it to be. Hess' law is confusing, although it seems simple. My major problem with all of these principles is knowing when to apply them. I think all I need to do is work more problems and I'll know whats going on. I think the lab we are doing next week will help a lot.

Weekly blog 11/4 thorugh 11/10

This week, we learned about vapor pressures, lattice energies, boiling points, and how intermolecular forces affect each of these. The higher the boiling point of a substance, the lower the vapor pressure. This means that the more intermolecular forces in a substance there are, the lower the vapor pressure in that substance. Lattice energy increases as ion size decreases and charge increases. This is a result of the coulombic relationship in lattice energy. Lattice energy is actually correlated with melting point, because ions in a lattice are harder to break from that lattice as lattice energy goes up. This means that when there is more lattice energy, the melting point rises. Here is a link to some good review on lattice energy.

On friday we applied all of these concepts we have learned in an activity where we had to determine if specific substances were or were not conductive, and also we had to identify unknown elements based on their properties. The conductivity test was fairly simple; we put a probe in each of the substances and it told us whether or not it was conductive. We discussed why some substances were conductive only when in a liquid state, like salt. Salt breaks into ions which can then conduct electricity when in liquid form. As for the identifying unknown elements, it was fun. It was interesting to see how some molecules were more viscous than others and to be able to tell which molecule was which just based on things like solubility, viscosity, and vapor pressure. Even though they all had virtually the same viscosity except glycerin, we could still figure it out. The key was testing the solubility with water.

My understanding of what was going on in class is pretty good, I think that I could still understand better why some things are conductive as a liquid but not as a solid. It seems counterintuitive to me, why something that has less density could be more conductive than something with more density. However, I think I'll be able to figure it out. Hopefully Dr. J will have another chat room open on monday night, because I found that enormously helpful when studying for the test last time.

Weekly Blog 9/28 through 10/3

We began this week focusing on metallic bonding. We learned that in metallic bonding, there is essentially a cluster of cations with a "sea of electrons" flying around the cations, not associate with any particular atom. Also, alloys are made in two different ways: interstitial or substitial. Interstitial is when smaller atoms fill the space in between larger atoms, making the alloy more dense, and substitutional alloys are where two similarly sized atoms are mixed, which does not increase density. Here, substitutional is on the left and interstitial is on the right.

Alloys are essentially solutions of metals.

We also learned about the intermolecular forces, or IMF's, that exist such as hydrogen bonding, dipole dipole bonding, and LDF's, or London Dispersion Forces. These are all van der Waals forces. Ion-dipole bonding can also happen, but this is not a van der Waal force. Ion-dipole forces are the strongest, then hydrogen bonding, then dipole-dipole, then the LDF's (induced dipole-dipole and induced dipole-induced dipole). We learned that LDF's are present in all molecules, polar, non-polar, ionic, everything. They are, however, very weak and don't compare much to hydrogen bonding and ion-dipole bonding. Here is a good site about LDF's.

Another thing we learned was about the hydration spheres of ions in a solution, We saw that if you dissolve K+Cl- in water, the K and Cl will separate and get surrounded by water molecules. The water molecules will align themselves so that the positive end is towards the negative ion and the negative end is towards the positive ion. The sphere will also include hydrogen bonding because of the two hydrogens in water bonded to the oxygen.

I think I have a good understanding of the ideas we covered this week. I'm looking forward to seeing what role entropy plays in these molecules and also learning more about what entropy really is. I've heard of it before, but I get the impression that I don't know anything significant about it.

Weekly Blog Post 10/20 through 10/27

On Monday, we began the week by reviewing for the exam on bonding. We reviewed amongst ourselves and went over a few problems from the review worksheet with the class. This was very helpful in getting to understand the concepts. That night, Dr. J put up a chat room in which we could ask questions of other students as well as Dr. J, which was extremely helpful. Being able to ask people questions you had rather than trying to figure it out yourself is super beneficial. Plus, it's nice to answer other people's questions to boost your confidence.

The next day we took the test, which was not extremely difficult but it had it's challenges. It was mostly conceptual, and I am fairly good at picturing things in my head so I did OK on it. I definitely mastered the concepts better than I thought I would be able to. 

Wednesday was mole day!

Dr. J made some delicious cookies and we had some hot chocolate while we talked for the whole class. We were assigned an essay about paintball and the role of polarity and hydrogen bonding in the paint balls and how scientists have made the paint water soluble without using water in the paint. 

We then started to learn about ionic bonding, which was an extended review of what we began to learn last year and had some more of it over the summer. It's not very difficult, but the POGIL we did covered a lot of material. I think I have a good understanding of ionic bonding so far. It's essentially just knowing what the tendency of each atom is; to become positive or negative. Just know that metals bond with nonmetals in ionic compounds. 

Last, we began a worksheet on metallic bonding but didn't get too far. I'm still pretty unsure about the whole thing, considering I only got about three questions done on the POGIL we got. The lecture and lecture quiz will help my understanding. 

My understanding of the material this week is good besides the metallic bonding. I learned a lot over the weekend (or, rather came to understand a lot) about covalent bonding through studying and the chat room. Those are very helpful. 

Weekly Blog 10/7 through 10/13

This week was a very busy week. We started it off with learning about vsepr models and how molecules are shaped by the bonded and non-bonded pairs of electrons. The vsepr models demonstrated why water has an irregular shape and why other atoms have their shapes. It also taught us how you can figure out the shape of the molecule knowing only the mount of bonded and unbonded pairs of electrons and the number of atoms around the central one. Here is a diagram of some vsepr structures.

We also learned about formal charges, which are used in Lewis dot diagrams in order to denote the charges of atoms. The formal charges are a result of polarity in a molecule, where one atom has more pull on the shared electron than the other. This can affect the vsepr structure of the molecule because of the way bonds are formed when an atom is polar. A molecule can be non-polar even if some of the bonds are polar. If the dipole moments all add to zero, then the molecule will have a net dipole moment of zero and will be non-polar. Here is a picture of a molecule and it's dipole moments.

At first I didn't understand polarity and dipole moments at all, but after I watched the lectures several times it began to make more sense. I have a much better understanding now than I did when I first watched the lecture. I still think that I need a lot more practice with it, however. Also, whiteboarding the Lewis structures and figuring out the molecular and electron domains was extremely helpful and I now know what I'm doing with those. Overall, my understanding of the material is good, but it can definitely be better.

Weekly Blog, 9/30 through 10/6

This week, we began with Lewis structures and things such as hypervalency and electron deficiency. We also focused on bond order with a POGIL that taught us the principle that as bond order goes up, bond energy goes up. Also, as bond length goes up, bond energy goes down due to coulombs law and how far away the electron cloud is from the other nucleus of the other atom. We learned the basics of coulomb's law last year in ACIS 2 or Sustainable Green Chem, I can't remember which. Here is a good video on bond order.

After we learned the bond orders and bond lengths, we moved on to our lab. Before the lab, we had to use stoich again to calculate the amount of nitric acid we would need to complete the reaction. Stoich, once again proving to be a very useful tool in chemistry. Next, we tested to find the amount of copper in a brass screw by using nitric acid to dissolve the copper overnight, and then testing the absorbency of the nitric acid, water, and copper solution using a colorimeter. We used the same technique that we used from the previous absorbency lab to find the absorbency, then we stopped until next week to chart the data because we could not get computers.

After the lab, we did a POGIL on vespr models. Vespr models are models used to show the shape of a molecule's geometry. WE modeled the shapes with balloons because balloons, like electron clouds, are succeptable to outside pressure and will distort if there is a force acting on them. For example, if there is a balloon pushing up agaisnt another balloon, it will push away due to tension. The same is true for an orbital, but it will be pushed away by repelling negative charges rather than pressure.

My understanding of the material this week is probably not up to where I need it to be. Formal charges are still very confusing to me, I do not really know how to make a proper Lewis structure with the formal charges. Finding the formal charges is easy enough, though. This coming week I'll need to work on that a little more to iron out the wrinkles.

Weekly Blog 9/22 through 9/29

This week, we started off with test prep for the first test on Wednesday. The first test was as hard as expected, and I suppose I didn't study enough for it. Those HotPots were a great way to study but they weren't enough to be able to do well on the test, as I now know. At least I know now how much I need to study in the future.

We were assigned new table groups and got new roles for pogils, as well. We tried them out later in the week. My role of recorder is actually a lot more difficult than I would have imagined, having to write and present the material. But, it forces me to learn so I like it.

After the test, we focused on Lewis models and Lewis structures in a pogil. These diagrams focus on how to represent the valence electrons of atoms and in turn how they bond with each other. They're also a good way to be able to see how atoms bond, and why some atoms are more easily bonded with than others. For example, the noble gases don't bond very often because of their full outer electron shell, and that is clearly shown in the diagrams. Here is a good link to how to make Lewis representations of atoms. It shows how to place the dots and how to label where bonding is ocurring. Lewis structures also are an application for electronegativity. The most electronegative atom will the in the center of the Lewis representation.

Lewis structures can be simple, but most are complex. It's mostly a problem of making sure there are the correct amount of valence electrons. I think I have the basic ideas down, but I could use some more practice, of course. I'm sure we'll be doing just that next week.

Weekly Blog 9/16 through 9/22

We began this week with a focus on limiting reactants and using stoichiometry to find which reactant was limiting the reaction. Limiting reactants seemed like it would be difficult before we actually learned how to do it. Stoichiometry seems to be very useful for a great amount of things with equations, in a simple way. Here is a great website for review of using stoich to limit reactants. We also did some practice particle diagrams to help us visualize the process of limiting reactants better rather than trying to look at cold numbers. 

To build off limiting reactants, we then learned how to use stoich to find the yield of reactions. Again, this seemed hard in theory but stoich made it very simple and easy to find the yield of reactions after you knew the limiting reactant. Yield is a simple concept and the only important thing about it is to find the limiting reactant in order to find theoretical yield.

This week was mostly practice with worksheets and whiteboarding, but we learned a lot. I feel like the whiteboarding is very useful because I get to see how everyone else does it and it also allows me to work with other people on problems, which helps me a great deal. There were no experiments this week, which is a bit of a disappointment as I love experiments. Oh well, there's always next week!

I'd say I have a solid understanding now of stoich and limiting reactants and finding yield. It's mostly just repurposing stoich to do different things, so once you have the base of it then you can do all the peripherals, I guess you could call them.

I don't have many pressing questions about this week except I do wonder what else can be done using stoichiometry. I'm sure we'll learn more about it next week or in the future. 

Weekly Blog 9/9 through 9/13

We began the week learning a new concept, stoichiometry. Also called stoich, it is used to find the amount of reactants needed or used in a reaction, as well as the amount of a product that is produced in a reaction. An essential concept to stoich is the mole ratio. This we learned during the previous week and over the weekend, and is used as the "bridge" in the stoichiometry process. The mole ratio itself is very simple; it is the ratio of the amount of one element to an another in moles. To practice stoich and mole ratios, we did a worksheet for homework that had several problems for us to practice. Here is a link to wikipedia for a good review of stoichiometry.

We also spent a couple days preparing for our lab on Thursday. We first learned what a good and productive beginning question is, for example, "How does temperature affect the percent transmittance of a solution?" Later that night we copied the procedure into our lab books. Some of us learned the hard way while copying that you are always to put the divider after the page you are using, or else you'll write through 20 pages. During the lab, we put to use our knowledge of Molarity and calculated the concentration of Blue #1 in both Powerade Mountain Berry Blast and Gatorade G2 Glacier Freeze. After we calculated the concentration, we used a calibration curve obtained through a stock dye of known concentration and found the absorption rate of the Blue #1 in the drinks. Once we had the absorption rate, we could calculate the concentration of Blue#1 dye in both the drinks using Beer's Law, A=kC.

After doing the experiment and other practice worksheets I feel as though I have a good understanding of what we have covered this week and how to apply it to situations. The thing I need to work on most is probably stoichiometry, although I think I have a deep enough understanding of it to be able to do it well.

One question I still have regarding the lab is how the temperature effects the rate of absorption of the solution. I realize the physical problems involved with doing this, such as the solution could heat up or cool down the cuvette and cause it to warp slightly, changing readings. Also, the temperature could be inconsistent throughout the trials so that would be difficult to regulate. This question is still puzzling to me and I have been thinking about it throughout the week, so I decided to put in the blog.