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BU CHEM 108 - Phase Diagrams and Properties of Water

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CHEM 108 1st Edition Lecture 4Factors Affecting Physical States (recap) - Intermolecular forces: Strength of attractive forces compared to kinetic energy of atoms/molecules. - Temperature: Affects kinetic energy of atoms/molecules. - Pressure: Affects distance between atoms/moleculesPhase diagram: - A graphic representation of the stabilities of physical states of a substance as a function oftemperature and pressure. - Equilibrium lines represent phase changes between solid/liquid, liquid/gas, and solid/gas under specific conditions (T, P).- Triple point: Temperature/pressure where all three phases coexist. - Critical point: Specific temperature/pressure at which the liquid and gas phases have the same density.- Supercritical region: fourth state of matter with properties intermediate between gas and liquid. It’s where Supercritical fluid exists; it’s a substance above its critical temperature and pressure. It has the density similar to that of a liquid but can penetrate materials like agas and dissolve substances in them like a liquid.- The slope of the lines represents the density of the substance at any given point on the line.- The phase diagram is different for different substances due to their unique chemical properties.The dotted green line is slanted to left; when that’s the case it means that density of the liquid is greater than the density of the solid. Just like in water.Properties of Water - Surface Tension: Resistance of liquid to any increase in surface area. o Molecules at surface have higher energy o Minimize surface  minimize energy. Like a sphere, it has minimal surface area/volume so it has less surface Tension- Factors Affecting Surface Tension o Intermolecular attractive forces, increase surface tension o Increase temperature, decrease surface tension. Raising the temperature of the liquid increases the average kinetic energy of the molecules the increased molecular motion makes it easier to stretch the surfaceo Ex: Objects float on water because it takes energy to break the water surface and water has high surface tension due to hydrogen bonding.- Viscosity: Measure of resistance of a liquid to flow.o Related to Intermolecular Forces: As attractive forces increase, surface tension and viscosity also increase. o Related examples: meniscus, capillary action- Cohesive forces: interactions between like particles. - Adhesive forces: interactions between unlike particles.o Ex: Capillary action: The rise of a liquid up a narrow tube due to adhesive forces between the liquid and the tube and cohesive forces within the liquid. o Meniscus: Curvature of liquid surface due to adhesive and cohesive forces: Concave: adhesive forces  cohesive forces (e.g., water on glass), • Convex: Cohesive forces > adhesive forces (e.g., mercury on glass).- Density of water: Density of water decreases when it freezes. H-bonding results in cage-like structure in solid state; less dense than liquid


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