Chapter3 Lecture

Chapter3 Lecture - Chapter 3 Learning objectives 1....

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Unformatted text preview: Chapter 3 Learning objectives 1. Introduce the concept of a pure substance 2. Illustrate property diagrams 3. Learn how to use data tables to obtain properties 4. Discuss ideal gas, real gas, and incompressible substance behavior Pure Substances A pure substance has a fixed chemical composition throughout A single chemical compound or element A mixture of various chemical compounds may also qualify as a pure substance as long as no changes in chemical composition occur Not good for mixtures that are not miscible (oil and water) Examples: Oxygen Water Air (gas mixture with constant composition) Copper Pure Substances: Phases A phase is a distinct molecular arrangement that is homogeneous throughout and separated from other phases by easily identifiable boundaries Solid (crystalline): Molecules are arranged in a three-dimensional pattern called a lattice that is repeated through space Molecules continuously oscillate about their equilibrium positions The velocity of the motions depend on temperature Dashed lines represent bonds and act like springs. Three degrees of freedom for vibrational motion. Pure Substances: Phases Liquids: Interactions between molecules less rigid Molecules do not have a fixed equilibrium location in space Molecular spacing is similar yet slightly larger to that of solids Rotational, translational motion occur Generally liquids have slightly lower density Gases: Molecules are far apart from each other Molecules move in random motion, colliding with each other and with walls of the container Fill the volume of the container V m Pure Substances: Phase Changes Consider a piston-cylinder device containing water. We will start at a temperature of 20 C and a pressure of 1atm and examine what happens to the substance as it is heated at 1 atm. All substances exhibit the same general behavior. 1. Compressed liquid (subcooled liquid) The water is not about to vaporize Based on observation, heat transfer to the system causes the temperature to rise and the fluid to expand (slightly) Pure Substances: Phase Changes 2. Saturated liquid A phase change from liquid to vapor is about to begin Any additional heating will produce some vapor Any heat loss (cooling) will bring the state away from the saturated state 3. Saturated liquid-vapor mixture Liquid and vapor phases coexist and are in equilibrium Additional heating causes more phase change from liquid to vapor Any heat loss causes phase change from vapor to liquid (condensation) Pure Substances: Phase Changes 4. Saturated vapor Only vapor phase is present Any heat loss will result in some of the vapor to condense into the liquid phase Any heat addition will result in an increase in temperature and expansion of the system 5. Superheated vapor A vapor that is not about to condense Addition of heat will cause an increase in the temperature and the system will expand Removal of heat will result in reduction of temperature and contract Pure Substances: Phase Changes Saturated liquid Saturated vapor constant m system closed , m V v Pure Substances: Phase Changes Repeat the experiment at several different pressures, obtain the following data....
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Chapter3 Lecture - Chapter 3 Learning objectives 1....

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