CH 102 1st Edition Lecture 3Outline of Current Lecture I. Energetics of Phase ChangesII. Melting Is Referred to as FusionIII. Heating Curve of a SolidIV. Heat of FusionV. Heating Curve for WaterVI. Water is an Extraordinary SubstanceVII. Phase DiagramsVIII. Supercritical FluidIX. Freeze DryingCurrent LectureI. Energetics of Phase Changesa. To go from one phase to another energy either is given to the substance or removed from the substanceb. The phase change from the solid to the liquid is melting and requires energy (ΔHfus, in J/mol or J/g)c. The phase change from the liquid to the gas is vaporization and requires energy (ΔHvap, in J/mol or J/g)II. Melting Is Referred to as Fusiona. As a solid is heated, its temperature rises and the molecules vibrate more vigorously.b. Once the temperature reaches the melting point, the molecules have sufficient energy to overcome some of the attractions that hold them in position and the solid melts (or fuses).c. The opposite of melting is freezing.III. Heating Curve of a Solida. As you heat a solid, its temperature increases linearly until it reaches the melting point.b. q = mass × Cs × ΔTc. Once the temperature reaches the melting point, all the added heat goes into melting the solid.d. The temperature stays constant.e. Once all the solid has been turned into liquid, the temperature can again start to rise.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.f. Ice/water will always have a temperature of 0 °C at 1 atm.IV. Heat of Fusiona. The amount of heat energy required to melt one mole of the solid is called the heat of fusion, ΔHfus.b. Sometimes called the enthalpy of fusionc. Melting is always endothermic; therefore, ΔHfus is (+).d. It is somewhat temperature dependent.e. ΔHcrystallization = –ΔHfusionf. Generally much less than ΔHvapV. Heating Curve for Watera. Heating 1.00 mol of ice at –25.0 °C up to the melting point, 0.0 °Cb. q = mass × Cs× ΔTi. Mass of 1.00 mol of ice = 18.0 gii. Cs= 2.09 J/g °C∙1. q = 18.0 g × (2.09 J/mol °C) × [0.0 °C – (–25.0 °C)]∙2. q = 941 J or 0.941 kJVI. Water is an Extraordinary Substancea. Water is a liquid at room temperature.i. Most molecular substances with similar molar masses are gases at room temperature.1. For example, NH3, CH42. This is due to H bonding between molecules.b. Water is an excellent solvent, dissolving many ionic and polar molecular substances.i. It has a large dipole moment.ii. Even many small nonpolar molecules have some solubility in water.1. For example, O2, CO2c. Water has a very high specific heat for a molecular substance.i. Moderating effect on coastal climatesd. Water expands when it freezes at a pressure of 1 atm.i. About 9%ii. Making ice less dense than liquid waterVII. Phase Diagramsa. Phase diagrams describe the different states and state changes that occur at various temperature/pressure conditions.b. Regions represent states.c. Lines represent state changes.i. The liquid/gas line is the vapor pressure curve.ii. On the line both phases exist simultaneously (i.e., in equilibrium with each other).d. Pointsi. The critical point is the farthest point on the vapor pressure curve.ii. Triple point is the temperature/pressure condition in which all three states exist simultaneously.iii. For most substances, the freezing point increases as pressure increasesVIII. Supercritical Fluida. As a liquid is heated in a sealed container, more vapor collects, causing the pressure inside the container to rise, the density of the vapor to increase, and the density of the liquid to decrease.b. At some temperature, the meniscus between the liquid and vapor disappears, and the states commingle to form a supercritical fluid.c. Supercritical fluids have properties of both gas and liquid states.IX. Freeze Dryinga. A kinder, gentler means of removing water from an aqueous solutioni. The solution is subjected to vacuum under a pressure less than 4.579 torr and cooled to less than 0 C, when upon it solidfies.ii. Upon heaying above 0 C the water sublimates away to the gas phaseiii. Used in concentrating food stuffsiv. Used in biology -