This week we started by delving back into IMF's, but this week we looked more at how they can affect and how they explain phenomena, such as surface tension, boiling point, evaporation rate, and viscosity of a liquid. We learned about how cohesive and adhesive forces affect all of these things and how they are affected by IMF's. We also looked at solids, including the two main groups of solid - crystalline and amorphous- as well as a couple of groups contained in those two - Ionic crystals, Covalent-network solids, and Molecular solids. We then looked at vapor pressure. Zach had a really good definition of vapor pressure, saying that it was about how many gas particles were moving at a given time and with what force. Thus, as vapor pressure increased, more molecules were moving in a gaseous state at a given temperature, so the higher the vapor pressure, the closer the substance is to boiling. Basically, the higher the temperature, the more particles have enough energy to escape the liquid and hang about as a vapor. Then we worked with lattice energy, which is the energy required to separate a mole of a solid ionic compound into its gaseous ions. It explains why the reaction forming an ionic compound is exothermic, and it is related to the charge and size of the ions. On Friday, we used everything we had learned about vapor pressure to try to figure out which compound was which given five chemical formulas and five liquids in dropper bottles. We used surface tension, viscosity, and evaporation rate to determine which compound was in which bottle.
I had a couple of questions. Why is it that you can pump something up as far as necessary but it can't be pulled up without a state change? What does enthalpy mean and why is it relevant? There was a question on the task chain for the test that had a phase graph - what was up with that graph? Which line were we supposed to be focusing on? I tried hard to participate in class this week. My group has changed, so my style of explanation has to shift as well, which has forced me to reexamine how I think about concepts. I understood everything fairly well in this section, although keeping the various relationships in order in my head was probably the most difficult part. I still need to work on my method of remembering which relationships correspond in which ways. This section has been fascinating, and I'm now trying to figure out why various substances have higher or lower surface tensions than others.
No comments:
Post a Comment