•solids • amorphous • crystalline • phase changes & diagrams · lecture 34 chapter 11...
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Lecture 34 Chapter 11 Sections 3 – 6
• Solids
• amorphous
• crystalline
• Phase changes & diagrams
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Solids
• In liquids and gases, molecules are free to move continually and randomly.
• In solids, particles are constrained to fixed positions.• Particles can only vibrate and occasionally rotate.• There are four major types (don’t worry about these too
much): – molecular solids– network solids– metallic solids– ionic solids
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Forces in Solids
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Amorphous vs. Crystalline
• Amorphous solids have fixed shapes, but have irregular internal shapes – no regular structure– plastics– glass (SiO2)– biological membranes
• Crystals have fixed shapes AND regular repeating structures.– NaCl– ice (H2O)– quartz (SiO2)
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SiO2 can be either
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Sock drawers can be either
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Amorphous or crystalline?
54321
Polycarbonate
25%25%25%25% 1. Amorphous
2. Crystalline3. Neither4. Both
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Amorphous or crystalline?
54321
Escher
25%25%25%25% 1. Amorphous
2. Crystalline3. Neither4. Both
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Amorphous or crystalline?
54321
Escher
25%25%25%25% 1. Amorphous
2. Crystalline3. Neither4. Both
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Network Solids of Carbon
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Phase Changes
• There are three states– Solid– Liquid– Gas
• A transformation from one state to another is called a phase change
• Each phase change is associated with a change in energy of the system
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• Notice that as a phase change occurs, temperature remains constant.
• A substance must completely change phase before the temperature of the system can increase (or decrease).
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Heats of Phase Changes
• Molar heat of vaporization, ∆Hvap: the heat needed to vaporize one mole of a substance at its normal boiling point.
• Molar heat of fusion, ∆Hfus: the heat needed to melt one mole of a substance at its normal melting point.
• Molar heat of sublimation, ∆Hsub: the heat needed to vaporize one mole of a substance from the solid phase (skips the liquid phase)
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Phase Diagrams
• Illustrate the relationship between phases of matter and the pressure and temperature
• The lines identify the conditions under which two phases exist in equilibrium
• Triple point – point at which all three phases coexist• Critical point – point at which one cannot distinguish
between a gas and a liquid– Beyond this is called a supercritical fluid.
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Phase Diagram
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Remember: You are done with the homework when you understand it!
Remember: You are done with the homework when you understand it!
Remember: You are done with the homework when you understand it!
Remember: You are done with the homework when you understand it!
Remember: You are done with the homework when you understand it!