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
