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UConn CHEM 1125Q - Phase Changes

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CHEM 1125Q 1st Edition Lecture 9Outline of Last Lecture (Ch. 12)I. Liquids and Solids, Melting Point, Vapor Pressure in Solids, Amorphous Vs Crystalline Solids, and Types of CrystalsOutline of Current Lecture (Ch. 12)II. Phase ChangesA. Types of Phase ChangesB. Liquid-VaporC. Solid-LiquidD. Solid-VaporE. Phase DiagramsIII. Current LectureII. Phase ChangesA. Types of Phase Changesa. A phase is a homogeneous part of a system that is separated from themain system by defined boundariesb. A phase change is simply the transition from one phase to anotherc. There are 6 phases:i. Freezing: liquid to solid, negative ΔHii. Melting: solid to liquid, positive ΔHiii. Evaporation (Vaporization): liquid to gas, positive ΔHiv. Condensation: gas to liquid, negative ΔHv. Sublimation: solid to gas, positive ΔHvi. Deposition: gas to solid, negative ΔHB. Liquid-Vapora. The Critical Temperature is the highest point at which a gas can be liquefied. Any temperature above that a gas cannot condenseb. The Critical Pressure is the minimum pressure needed to liquefy a substance at its critical temperatureC. Solid-Liquida. Melting is also known as fusionb. The melting/freezing point of a substance is the temperature at whichthe solid and liquid phases coexist in equilibriumc. The molar heat of fusion (ΔHfusion) is the amount of energy needed to melt 1 mole of a solidD. Solid-VaporThese 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.a. Carbon dioxide is almost never found as a liquid, and mainly changes between the gas and solid phases, known as sublimation and depositionb. ΔHsublimation = ΔHfusion + ΔHvaporizationE. Phase Diagramsa. A phase diagram is a graph depicting the phases and phase changes for a substance based on temperature (x-axis) and pressure (y-axis). It shows the conditions at which a substance exists as a solid, liquid, gas,or even multiple phasesb. The Triple Point on a phase diagram is the only point on the graph where the 3 phases of a substance exist together at


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