e97mtm - Engineering 45 The Structure and Properties of...

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Engineering 45 The Structure and Properties of Materials Midterm Examination April 3, 1997 Problem 1: (a) Describe the ß-ZnS structure, either in words or pictures. (b) The ß-ZnS structure is a common structure for compound semiconductors, such as GaAs. Why might you expect this? (c) The ß-ZnS structure is also adopted by ionic compounds, including some of the silver halides. Why might you expect this? Suggest a simple criterion that explains why some ionic compounds might prefer the ß-ZnS structure to the CsCl or NaCl. Problem 2: The Second Law of Thermodynamics states that the entropy of an isolated system can only increase. The change in entropy in an infinitesimal change of state is dS = 2.1 where T is the temperature, E is the internal energy, P is the pressure, V is the volume, µ k is the chemical potential of the k th component and N k is the mole number of the k th component. (a) Let two solids have fixed volumes and chemical contents, and let their
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e97mtm - Engineering 45 The Structure and Properties of...

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