Our new unit is chemical equilibrium. To explore this topic before being officially introduced to it, we used the simulation and a few POGILs. I think that this is a good way of being introduced to something new, as it helps you get familiar with the topics by introducing similar things and starting off very basic. To reflect on these pogils I thought they were very useful in helping me get a good head start on the topic of equilibrium. Basically equilibrium is based on a major concept:
A reaction can go both ways - the forward and the reverse reactions.


At equilibrium, the overall rates at which the forward and reverse reactions occur are equal. Once equilibrium is reached, the concentration of the reactants and the products doesn't change because the rates are equal:

The most important concept in equilibrium is the equilibrium constant. The equilibrium constant, K_eq, is the concentration or the partial pressure of the products, raised to their stoichiometric coefficients, divided by the concentration/partial pressure of the reactants, raised to their stoichiometric coefficients. If this number is less than one, there are more reactants than products at equilibrium. If this number is greater than one, there are more products at equilibrium.

The second important concept is Le Chatelier's Principle. This states that if a system at equilibrium is disturbed, the reaction will shift in order to go back to equilibrium. There are three such disturbances:
     1. Changing the concentration of a reactant/product: If we add more reactant, the reaction will shift to the right, in order to make more products, and vice versa. In this instance, K_eq does not change because the ratio of concentrations is preserved.
     2. Changing the volume of the vessel: If we decrease the volume, the pressure will increase, so the reaction will shift to the side with less moles in order to lower the pressure back to the original, and vice versa. Again, in this case, K_eq does not change.
      3. Changing the temperature: This is the only way to change the equilibrium constant. If reaction is endothermic, and we increase the temperature, more products will be made, and K_eq will increase, and vice versa.
      To reflect on this, I think this principle is essential to equilibrium as a whole and I definitely need to understand it more. I came after school a couple of times to work on the equilibrium worksheets and I think I have a very good understanding of how to do most of the calculations in this unit. Rice tables are very easy for me now and I think that is a big part of this unit.


Adding a catalyst to the reaction will not change anything except the rate of the reaction. It will, however, change increase BOTH the forward and reverse reaction, making the reaction achieve equilibirium faster.

It is important to remember that solids and liquids do not play a role in the calculation of the equilibrium constant. Their concentration or partial pressure is always constant, and since K_eq is a ratio, they end up cancel out.

The last concept we learned was the relationship between thermodynamics and equilibrium. This was confusing at first, but now I understand it better, although I don't know how to answer some of the questions on the Equilibrium III worksheet. There is a relationship between Gibbs Free Energy and the equilibrium constant:

ΔG0=−RTlnK

To reflect on this entire unit as a whole, it definitely has not been as hard as I imagined it would be. I thought there would be very difficult calculations and the concepts would be extremely hard. So far, I've gotten down the calculations fairly easily, and although the conceptual stuff is pretty difficult, I am definitely starting to get it more.

ΔG0

            This week in class we did a full review of everything that has to do with gases. and did some demonstrations with liquid nitrogen, which was probably the most exciting thing we've done in AP chemistry thus far. We did a lot of whiteboarding of problems involving ideal gases and real gases. 

            The bulk of the week was spent working on problems from the Gases I and Gases II worksheets. The Gases I worksheet had a lot to do with problems that involved the ideal gas equation. This is PV=nRT. We can manipulate this equation to solve for any one of the four variables that can affect gases. An ideal gas is not something we actually see in real action but is just a hypothetical gas whose pressure, volume, and temperature can be described by this equation.  We also discussed a little bit the effects of STP and what it is exactly. STP is the standard temperature and pressure conditions of gases at 0° C and 1 atm. The volume of STP conditions is 22.4 L. We also faced some problems where P, V, and T all changed for a constant number of moles. When this happens we can set up an equation where P₁V₁/T₁=P₂V₂/T₂. This equation is very helpful for finding a final variable if we know all the initial variable’s and two of the final variables or vice versa for finding an initial variable. In reflection, these worksheets were very confusing and hard to complete at first, but after several sessions of whiteboarding I began to understand a little more.

            We also looked at some further applications of the ideal gas law. This involved density and molar mass. Since D=M/V we can substitute in variables for volume if we need to do so. We also know that molar mass is equal to mass per one mole of substance. We can use this knowledge to rework our ideal gas equation to solve for molar mass and density of gases. To reflect on this, I thought the ideal gas law was fairly simple and didnt involve that much thinking.

            We also touched on effusion and diffusion. Effusion is the escape of molecules through a tiny hole into an evacuated space. Diffusion is the spread of one substance throughout a space or throughout a second substance. There is an equation that is the same for both effusion and diffusion. We can use this equation to help solve for the identity of a gas based on its molar mass. I thought effusion and diffusion were pretty simple because the equations for them were very simple and not hard to work. 

            The last matter that we discussed was the deviation of real gases from ideal gases. This can be recognized by Van der Waal’s equation that corrects the ideal gas equation due to the finite volume occupied by the actual gas molecules and for the attractive forces that are present between gas molecules. This basically raises the pressure and lowers the volume. In reflection this concept was pretty easy to understand and apply.

            To reflect, this week was very hard for me because the gases unit is a pretty hard one in general, I did a lot of review this weekend and understand the topics much more than I did before but still need more work before the test. I thought the whiteboarding during the week also definitely helped me understand what was going on with the worksheets. The liquid nitrogen demo was very exciting and educational and was my favorite part of the week for sure.

A 12 minute video regarding effusion and diffusion