Ch 101 1st Edition Lecture 17 Outline of Last Lecture I Partial Pressure II Intramolecular Forces III Intermolecular Forces A Dispersion Forces B Dipole Dipole C Hydrogen Bonding IV Determining Polarity Outline of Current Lecture I States of Matter A Liquid B Gas Current Lecture I States of Matter Matter has three forms solid liquid and gas The relationship between these states of matter are shown through phase diagrams that show how the pressure and temperature correlate with the states of matter The diagram tells us that solids exist in low temperature environments Liquids are somewhere in the middle because in high low pressure or temperature conditions they will undergo a phase change and gas likes higher temperature at a lower pressure These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Another way to look at phase change is to look at a diagram that shows you the phase change as the temperature and energy rises This graph is important because it shows you that during a phase change the substance doesn t change temperature This graph also tells you that you have to increase the energy to go from a solid to a liquid to a gas Dynamic Equilibrium The Dynamic equilibrium is the temperature at the freezing melting point 0oC where the substance exists as both a solid and a liquid Boiling Point The boiling point is the temperature where the vapor pressure equals the external pressure it is where the substance exists as a liquid and a gas Heat of Fusion The heat of fusion is represented by Hfus and it is the amount of heat required to melt a substance at the substances melting point A liquid that requires a lot of energy or a high heat of fusion has strong intermolecular forces A Liquid Cohesive Force Cohesive forces is the reason liquids have viscosity and surface tension Cohesive means that something sticks to itself more than it wants to stick to other things Viscosity is the resistance of a liquid to flow The resistance is caused by the liquid having large molecules that become tangled in each other Liquids like syrup has a high viscosity where liquids like vinegar has a low viscosity Surface tension is the energy required to increase the surface area of a liquid Water has a higher surface tension because it beads together it sticks to itself more and requires more energy to increase the surface area Liquids like acetone has low surface tension therefore it spreads out and runs everywhere instead of beading up like water Adhesive Force Adhesive forces are forces that make a liquid attracted to other molecules Adhesive forces is the reason water forms a meniscus when put in a glass A meniscus is the concave or convex divot that in formed when a liquid is poured into a glass Substances with strong adhesive forces create a concave meniscus that is concave up and substances with weak adhesive forces form a convex meniscus that is concave down B Gas Dew Point The temperature where water vapor starts to condense into a liquid Vapor Pressure Vapor pressure is measured by the pressure of the vaporized molecules on the liquid The more vaporized molecules the higher the vapor pressure Liquids with high vapor pressure also have weak intermolecular forces that are easily broken to allow the liquid to vaporize quickly Heat of Vaporization The heat of vaporization is represented by Hvap and is the heat required to vaporize a substance at the substances boiling point Relative Humidity To determine the humidity you need to first view this chart Then use the equation Observed Pressure Maximum Pressure 100 Relative Humidity