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Charles's law: The V-T relationship under constant pressure
Gas Laws: Charles's Law
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Let's now explore the relationship between the volume and temperature of a gas at constant pressure and particles.
To fully understand this relationship it's important to recognize the relationship between the temperature and the speed at which molecules move. Run the simulator below (click Run) and then slowly increase the temperature (increase the temperature by clicking on the red triangle). Continue raising the temperature until the red bar reaches the top.
Stop the simulator. Hopefully you noticed that as we increase temperature, molecules move faster (more exactly, we can say that their kinetic energy has increased). With this fundamental knowledge in our backpocket, let's now see how this relates to the relationship between volume and temperature. In the simulator below, we will increase the temperature while we keep the pressure and particles of gas constant.
Instructions:
1. Click the Increase Temperature button to slowly increase the temperature (note that the piston will respond to the temperature increase so as to maintain a constant pressure). Observe how the volume changes as we increase the temperature. Let the simulator run until it stops automatically.
3. Take a snapshot of the graph as you did on the previous page. When the Add Snapshot dialog box appears, type "Volume vs. Temperature at constant pressure and moles" in the box below the snapshot. Click OK.
As we increased the temperature, we discovered that the volume increased because the strength of the collisions with the container walls increased. Note that the pressure did not increase because the piston was able to respond to the increased strength of collisions by expanding the container size.
This direct relationship between temperature and volume is known as Charles's law. Later in this activity, we'll see how Charles's law explains how hot air balloons work. For now take a look at the demonstration linked below. Very cold liquid nitrogen (-196 oC or 77 K) will be poured over a balloon filled with air (before you look at it, can you guess what is going to happen to the balloon?).
Click here for demo. (publisher video is linked; I'm scheduled to make an in-house video of it on Wednesday)
Did the balloon behave as you expected? Hopefully you recognized that it followed Charles's law by losing considerable volume as the cold liquid nitrogen was poured over it. When the liquid nitrogen was removed, the volume of the air then increased as the temperature of the gas slowly returned to room temperature.
Let's now move on to a related gas law. One where we'll explore the relationship between temperature and pressure.
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