Author: yasir
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Translational Kinetic Energy
We again consider a single molecule of an ideal gas as it moves around in the box of Fig. 19-3, but we now assume that its speed changes when it collides with other molecules. Its translational kinetic energy at any instant is mv2. Its average translational kinetic energy over the time that we watch it is in which we…
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Pressure, Temperature, and RMS Speed
Here is our first kinetic theory problem. Let n moles of an ideal gas be confined in a cubical box of volume V, as in Fig. 19-3. The walls of the box are held at temperature T. What is the connection between the pressure p exerted by the gas on the walls and the speeds of the molecules? The molecules of gas…
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Ideal Gases
Our goal in this lesson is to explain the macroscopic properties of a gas—such as its pressure and its temperature—in terms of the behavior of the molecules that make it up. However, there is an immediate problem: which gas? Should it be hydrogen, oxygen, or methane, or perhaps uranium hexafluoride? They are all different. Experimenters…
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Avogadro’s Number
When our thinking is slanted toward atoms and molecules, it makes sense to measure the sizes of our samples in moles. If we do so, we can be certain that we are comparing samples that contain the same number of atoms or molecules. The mole is one of the seven SI base units and is defined as…
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The Kinetic Theory of Gases
What crushed the tank car during the night? The interior of this railroad tank car was being cleaned with steam by a crew late one afternoon. Because the job was unfinished at the end of their work shift, they sealed the car and left for the night. When they returned the next morning, they discovered…
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Heat Transfer Mechanisms
We have discussed the transfer of energy as heat between a system and its environment, but we have not yet described how that transfer takes place. There are three transfer mechanisms: conduction, convection, and radiation. Conduction If you leave the end of a metal poker in a fire for enough time, its handle will get…
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Some Special Cases of the First Law of Thermodynamics
Here we look at four different thermodynamic processes, in each of which a certain restriction is imposed on the system. We then see what consequences follow when we apply the first law of thermodynamics to the process. The results are summarized in Table 18-5. 1. Adiabatic processes. An adiabatic process is one that occurs so rapidly or occurs…
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The First Law of Thermodynamics
You have just seen that when a system changes from a given initial state to a given final state, both the work W and the heat Q depend on the nature of the process. Experimentally, however, we find a surprising thing. The quantity Q − W is the same for all processes. It depends only on the initial and final states and does…
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A Closer Look at Heat and Work
Here we look in some detail at how energy can be transferred as heat and work between a system and its environment. Let us take as our system a gas confined to a cylinder with a movable piston, as in Fig. 18-13. The upward force on the piston due to the pressure of the confined gas…
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The Absorption of Heat by Solids and Liquids
Heat Capacity The heat capacity C of an object is the proportionality constant between the heat Q that the object absorbs or loses and the resulting temperature change ΔT of the object; that is, in which Ti and Tf are the initial and final temperatures of the object. Heat capacity C has the unit of energy per degree or energy per kelvin. The heat capacity C of, say, a…