Homework Exercise 8.43 and Phase Changes

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Liz White 1K
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Joined: Thu Jul 13, 2017 3:00 am

Homework Exercise 8.43 and Phase Changes

Postby Liz White 1K » Fri Jan 26, 2018 3:52 am

Exercise 8.43 mentions the connection between values such as heat of fusion and heat of vaporization, as well as heat capacities for different phases, and relates them to the appearance of phase change graphs. Can someone refresh me on how to read and interpret heating curves, and how to relate certain lines to certain values? More specifically, which value connects to which line, and how can that be explained? Thanks.

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

Re: Homework Exercise 8.43 and Phase Changes

Postby Kelly Kiremidjian 1C » Fri Jan 26, 2018 10:19 am

When looking at a heating curve, you have heat supplied on the x axis and temperature on the y axis. The plateau's represent the phase change. The first plateau is solid changing to liquid, and the second plateau is liquid changing to gas. Notice there is no temperature change during the phase changes. The parts with increasing slope indicate temperature change.

Looking at #43, they give deltaHfus and deltaHvap. These are the kJ.mol-1 used during the plateaus. Since you know the values, you can determine which graphs would be accurate based on the length of the plateau's and the corresponding deltaH values. We are also given heat capacities. For the heat capacity of a solid, you would look at the sloped region before the first plateau. For the heat capacity of a liquid you would look at the sloped region between the first and second plateau. For the heat capacity of the gas you would look at the sloped region after the second plateau. Based on the steepness of the slopes and corresponding heat capacities you can determine which graph is most accurate.

Hope this helps


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