11-11-13

This week we learned about vapor pressure, lattice energy, and reviewed for the test this Tuesday.

Gas particles hit surfaces with a certain amount of force. They all have mass and must stop when they hit a surface (which is acceleration). The more gas particles, the more force. Vapor is the gas state of a liquid at room temperature, and it exhibits a pressure just like any gas. As temperature rises, the fraction of molecules that have enough energy to escape increases (warmer liquid evaporate faster). The more molecules that escape, the higher the pressure they exert. A liquid reaches boiling point when the temperature at which it's vapor pressure equals atmospheric pressure. Vapor pressure increases as temperature increases because more and more molecules at the surface have enough kinetic energy to escape the surface. At higher altitudes, water boils at a lower temperature so cooking and baking lengths are longer. The higher the boiling point, the lower the vapor pressure and the lower the boiling point the higher the vapor pressure. Vapor pressure decreases with molecular weight, but boiling point increases. If the intermolecular forces increase, vapor pressure decreases.

Lattice energy is the energy required to completely separate a mole of a solid ionic compound into its gaseous ions. The energy associated with electrostatic interactions is led by Coulomb's law. Lattice is periodic and predictable because charge and ion size are periodic in nature. It increases with the charge of ions. It also increases with decreasing size of ions. As lattice energy increases, so does melting point. Smaller ions lead to increased lattice energy. Greater charge also leads to increased energy, and the effect of charge is greater than the effect of distance.

We also did an activity where we tested the conductivity of substances with LED conductivity testers that light up when a substance or solution is conductive. Through this activity we determined that steel was the only one that conducted electricity because the electrons are loosely held due to metallic bonding. Water, acetone, ethanol, and nonane were all poor conductors because they are covalently bonded, making the electrons unable to move around. Another activity we did was identifying six unknowns by comparing surface tension and viscosity. My group was fairly close and predicted 4/6 of the substances.

I'd give my understanding this week about an 8. I definitely understand lattice energy and surface tension and how they affect bonding and was able to explain it to my classmates when they asked. I'm still not quite totally sure about everything on vapor pressure and I especially noticed while doing the task chains. The easiest part to me is the water phase change diagram and identifying what's happening in the diagram at a certain point and when a change is endothermic or exothermic like in the task chains.