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# ln2s08 - Lecture 2 Phase Diagrams It is particularly...

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Lecture 2: Phase Diagrams It is particularly instructive to assemble graphs and diagrams that contrast the properties of a compound's phases. For example, the phase diagram that is most famous is a plot of pressure vs. temperature in which the various states of matter are identified. We will be examining this kind of plot, along with two others, in this section of the notes. Presented below are three ways we can draw a phase diagram: certainly the simplest is a triangle with the 3 phases at the vertices and the names of the phase changes along the sides of the triangle. Although simple, if you can actually draw this from scratch and assign the phase and associated thermodynamic sign changes that you learned in Chapter 6, then you know quite a bit: s ! g sublimation, Δ H+, Δ S+ g ! s deposition, Δ H-, Δ S- solid liquid In chapter 6 you learned about the calculation of Δ H at phase transitions and over temperature intervals in which you use C Δ T to find Δ H have seen time dependent phase changes. You will learn to perform calculations of how much heat is added or removed as a material transitions from one phase to another. Note that there are five different constants for five different calculations to determine the energy change. The total energy change is determined by adding up the individual energy changes over the temperature range. C solid which is used in a Δ H = mC Δ T Δ H fus which is a molar quantity that needs to be scaled to the amount of material to find the heat change C liquid which is used in a Δ H = mC Δ T Δ H vap which is a molar quantity that needs to be scaled to the amount of material to find the heat change C gas which is used in a Δ H = mC Δ T s ! l melting, Δ H+, Δ S+ l ! s freezing, Δ H-, Δ S- gas l ! g vaporization, Δ H+, Δ S+ g ! l condensation,

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