CHEM 1221 1st Edition Lecture 3Outline of Last Lecture I. Intermolecular ForcesOutline of Current Lecture II. Ion-Dipole forcesIII. Properties of Liquidsa. Viscosityb. Surface tensionIV. Adhesive/Cohesive Forcesa. Capillary ActionV. Phase Changesa. Energy changesCurrent LectureIon-Dipole Forces: Cations or anions are attracted to the oppositely charged pole of a polar molecule.Ex.) When salt is dissolved in water Na+ cation is formed along with Cl- anion. The water molecules form around the ions, Na+ attracts the negative part of the water molecule and the Cl- attracts the positive part of the water molecule, creating a weak intermolecular bond known as an Ion-Dipole Force.The magnitude (number of charge) of an ion-dipole interaction depends on:1. Size of the ion2. Magnitude of ion charge3. Magnitude of the dipole momentProperties of Liquids: Viscosity: The resistance of a liquid to flow, greater the viscosity the liquid flows more slowly.- The smaller the molecules, the more easily they slide past each other so in result the smaller the viscosity.Ex.) When water (small molecule) is put into a cold pan 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.its spreads around easily. (Low viscosity) When oil (large molecule) is put into a cold pan it tends to keep its shape (High viscosity).- Not as important as the size, but stronger intermolecular forces also increase viscosity.- How does temperature affect viscosity?o When you increase temperature molecules move faster so in result as temperature increases viscosity decreases.Surface Tension of Liquids:- A liquid’s main goal is to minimize its surface area. It achieves this goal by forming a spherical shape.o Water’s property is different, because gravity pulls it down a waterdroplet flattens out.o The droplets are formed because the molecules on the surface have fewer places to interact and form intermolecular forces with other molecules.Surface Tension: Energy required to increase the area of a liquid. Measured in J/m2- The greater the Intermolecular force, the greater the surface tension.Adhesive/Cohesive Forces: Adhesive- force of attraction between a liquid and a solidCohesive- force of attraction between a liquid and a liquid- If adhesive forces are greater than cohesive forces the liquid spreads out- If the cohesive forces are greater than the adhesive forces then the liquid will bead up (create droplets)o Ex.) When water is put into a glass tube, the adhesive forces are stronger then the cohesive forces (water will spread out). So waterwill try to maximize its adhesive forces, creeping up the glass tube and forming a meniscus.o Ex.) When mercury is put into a glass tube, the cohesive forces arestronger than the adhesive forces (form droplets). Since mercury is trying to minimize the adhesive forces it creates a reverse meniscus.Capillary Action: very small glass tube where water is sucked up the tube due to the adhesive force.Phase Changes:Phase transition Name Solidliquid Melting, fusion Liquidsolid Freezing Liquidgas Vaporization Gasliquid Condensation, liquefaction Solidgas Sublimation Gassolid Deposition Energy Changes: - Energy is required to convert a liquid to a gas- Energy is released when gas is converted to a liquido These happen because bonds are being broken/formed- When a liquid is converted to a gas the intermolecular forces are broken (Vaporization- When a gas is converted to a liquid intermolecular forces form (Condensation)- Molar heat of fusion: The heat energy required to melt one mole of a solid.- Molar heat of vaporization: The heat energy required to vaporize one mole of a liquid.o The molar heat of fusion is always smaller than the molar heat of
View Full Document
Unlocking...