These past weeks in AP Chemistry we have worked on the unit of gas laws. These laws, formed long ago, define the interactions between the many properties of any system of gas. Our lesson included both theoretical calculations as well as more complicated real-world calculations, with far more accurate results. As usual, we were first given the information through online lectures, allowing us to pause and repeat sections, followed by a simple quiz to test our overall understanding of the information and for our teacher to see the points in the lecture that did not properly explain themselves. We followed these up in class with ConcepTests, which are taken in the open, each student holding up the number of fingers corresponding to their answer, for the teacher to find and solve the areas in which multiple students are still having the most difficulty. I personally found this very useful because, although I understand the main concept areas already, it helps me to see which spots are most problematic for me and my peers in regards to simple mistakes due to negligence.
We used an online PHeT simulator to initially introduce us to ideal gas situations and interactions. We filled out a pre-made Google Doc spreadsheet in order to find the relationships on our own, before learning about them. This was very useful way to offer the students a much more realistic look into the way science works outside of the classroom: data is gathered in as high volume as possible, and then pulled in together and analyzed as a whole. Through this process we were able to easily be guided into finding Boyle's, Charles', and Guy Lussac's laws of ideal gas interactions of various properties. We were later guided into finding the Combined Gas Law, stating that the product of pressure and volume divided by the temperature of a gas will always equal a constant. We continued by adding n (number of moles) into the mix. Through further data collection from the simulator you could find that the number of moles was directly proportional to pressure or volume, while it was inversely proportional to temperature, given in the well known equation PV = nRT, where R is a constant coefficient. For further practice see the link below.
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Classmate holds balloon of oxygen gas in liquid
nitrogen changing the volume |
After learning all about ideal gas situations, we were told that this was not exactly how the world worked. We had previously assumed in our calculations that all particles had volumes of zero and there were no interactions between the different molecules in the container, which is not the case due to intermolecular forces (covered in an earlier blog). In reality, substances contain dipole-dipole, dipole-induced dipole, London dispersion and hydrogen bonding interactions, in different combinations. These in turn attract all particles within a system toward each other, decreasing the overall pressure of the system. Similarly, every particle has a small but significant volume, which increases the overall volume of the system. We learned that in order to calculate more accurate values you must find the constant for each molecule and incorporate it into the equation.
Practice with Gas Laws:
http://www.sciencegeek.net/Chemistry/taters/Unit5GasLaws.htm
