LectureT3

LectureT3 - 5/13/2004 H133 Spring 2004 1 Chapter 3: Gas...

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Unformatted text preview: 5/13/2004 H133 Spring 2004 1 Chapter 3: Gas Processes In this chapter we want to continue to discuss gases. We developed the ideal gas law in chapter 2 Now we want to understand some of the processes that occur as we change the P, V or T of a gas We will also be interested in what happens as we add or subtract thermal (internal) energy from the system. Once again it is important to establish rigorous definitions before we start to consider the physical phenomena. In this case we need to make sure we have strict definitions of work and heat. Heat: This is the flow of energy across a boundary between to systems (objects) that are in thermal contact and a temperature difference exists between them KEY POINT: KEY POINT: Work: Any other flow of energy across a boundary that is not considered heat Example: Important: T Nk PV B = 5/13/2004 H133 Spring 2004 2 Q (heat) or W (work) or k-W?? This is exercise T3X.1 and T3X.2 in Moore: Using a Q to label heat and W to label W, classify each of the case below: Soup (B) in a pan on an electric stove (A) gets hot You (A) compress air (B) in a bike pump, making it warm. Your hands (A) are warmed when they face a fire (B). The atmosphere (A) warms a reentering spacecraft (B). A hot pie (A) becomes cooler while sitting in the kitchen (B). Your chair (B) becomes warmer after you (A) sit in it for a while. A drill bit (B) becomes hot after being spun by a drill (A) Using a W for thermal work and a K for k-work, classify each case below: The total Kinetic Energy of the molecules in a gas bottle increase as the bottle falls in a gravitational field. The total Kinetic Energy of the molecules in a gas bottle increase as the gas is stirred with a fan in the bottle. Air drag on a falling meteorite causes the meteorites temperature to increase. Air drag on a falling meteorite causes it to slow down (lose kinetic energy) Gas in a bottle gains energy from a spark. A small pellet is vaporized by a laser beam. 5/13/2004 H133 Spring 2004 3 Q vs W We must be a little bit careful when classifying Q and W. The distinction between the two is a little bit artificial and depends on how we are defining the boundary of our system. Moore has a good example with an electrical circuit through water as shown below. Case A: We define the water, the container, and the resistor as the system. Case B: We define the water alone to be the system....
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This note was uploaded on 06/03/2011 for the course H 133 taught by Professor Furnstahl during the Spring '11 term at Ohio State.

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LectureT3 - 5/13/2004 H133 Spring 2004 1 Chapter 3: Gas...

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